<PAGE>   1

                                                                    EXHIBIT 10.1

                            ASSET PURCHASE AGREEMENT

                                      among

                        CAPSTONE VENTURES SBIC, L.P. and

                             AI RESEARCH CORPORATION

                                   as Sellers

                                       and

                                 PLANETCAD INC.
                                  as Purchaser

                            Dated as of June 1, 2001
<PAGE>   2
                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                        Page
                                                                                        ----
                                    ARTICLE I


                      Purchase and Sale of Acquired Assets
<S>                  <C>                                                               <C>
SECTION 1.01.        Purchase and Sale...............................................    1
SECTION 1.02.        Acquired Assets and Excluded Assets.............................    1
SECTION 1.03.        Excluded Liabilities............................................    2
SECTION 1.04.        Consents of Third Parties.......................................    3
SECTION 1.05         "As Is" Condition ..............................................    3

                                   ARTICLE II

                                   The Closing

SECTION 2.01.        Closing Date....................................................    3
SECTION 2.02.        Transactions To Be Effected at the Closing......................    3

                                   ARTICLE III

                    Representations and Warranties of Sellers

SECTION 3.01.        Organization, Standing and Power................................    4
SECTION 3.02.        Authority; Execution and Delivery; Enforceability...............    4
SECTION 3.03.        No Conflicts; Consents..........................................    4
SECTION 3.04.        Assets Other than Intellectual Property, Technology, Software
                         and Internet Domain Names...................................    4
SECTION 3.05.        Intellectual Property; Technology; Internet Domain Names;
                         Software....................................................    5
SECTION 3.06.        Contracts.......................................................    6
SECTION 3.07.        Sufficiency of Acquired Assets..................................    6
SECTION 3.08.        Taxes...........................................................    7
SECTION 3.09.        Proceedings.....................................................    7
SECTION 3.10.        Compliance with Applicable Laws.................................    7
SECTION 3.11.        Disclosure......................................................    7

                                   ARTICLE IV

                   Representations and Warranties of Purchaser

SECTION 4.01.        Organization, Standing and Power................................    8
SECTION 4.02.        Authority; Execution and Delivery; and Enforceability...........    8
SECTION 4.03.        No Conflicts; Consents..........................................    8

                                    ARTICLE V

                                    Covenants

SECTION 5.01.        Confidentiality.................................................    9
SECTION 5.02.        Best Efforts....................................................    9
SECTION 5.03.        Expenses; Transfer Taxes........................................    9
SECTION 5.04.        Brokers or Finders..............................................    9
</TABLE>



                                        i
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<TABLE>
<S>                  <C>                                                                <C>
SECTION 5.05.        Post-Closing Cooperation........................................    9
SECTION 5.06.        Publicity.......................................................   10
SECTION 5.07.        Further Assurances..............................................   10
SECTION 5.08.        Names and Internet Domain Names Following Closing...............   10

                                   ARTICLE VI

                        Actions and Deliveries at Closing

SECTION 6.01.        Sellers' Actions and Deliveries at Closing......................   10
SECTION 6.02.        Purchaser's Actions and Deliveries at Closing...................   11
SECTION 6.03.        Amendments and Waivers..........................................   11

                                   ARTICLE VII

                                 Indemnification

SECTION 7.01.        Indemnification by Sellers......................................   12
SECTION 7.02.        Indemnification by Purchaser....................................   12
SECTION 7.03.        Termination of Indemnification..................................   12
SECTION 7.04.        Procedures......................................................   12
SECTION 7.05.        Survival of Representations.....................................   13

                                  ARTICLE VIII

                               General Provisions

SECTION 8.01.        Assignment......................................................   13
SECTION 8.02.        No Third-Party Beneficiaries....................................   13
SECTION 8.03.        Attorney Fees...................................................   14
SECTION 8.04.        Notices.........................................................   14
SECTION 8.05.        Interpretation; Exhibits and Schedules; Certain Definitions.....   15
SECTION 8.06.        Counterparts....................................................   15
SECTION 8.07.        Entire Agreement................................................   15
SECTION 8.08.        Severability....................................................   15
SECTION 8.09.        Governing Law...................................................   15
SECTION 8.10.        Dispute Resolution .............................................   16
</TABLE>


Exhibit A         Form of Warrant

Company Disclosure Schedule

                                       ii
<PAGE>   4
                            ASSET PURCHASE AGREEMENT

         THIS ASSET PURCHASE AGREEMENT dated as of June 1, 2001, is hereby
entered into by and among CAPSTONE VENTURES SBIC, L.P., a Delaware limited
partnership, AI RESEARCH CORPORATION, a California corporation (each referred to
herein as "Seller" and collectively as "Sellers"), and PLANETCAD INC., a
Delaware corporation. ("Purchaser").


                                    RECITALS

         WHEREAS, on March 12, 2001 pursuant to that certain Intellectual
Property Security Agreement dated December 12, 2000 (the "Security Agreement"),
Sellers acquired from CastaLink.com, Inc., a California corporation
("CastaLink") all right, title and interest in and to, and all the assets
related to, the suite of software products, including all operating and
applications computer software programs, known as electronic Collaborative
Application Solution, including the software applications known as LinkSpan,
eOrder, eSalesForce, eConnect, eBizRules, eAnalysis, eMessaging and eSupply,
which software is designed to allow customers and suppliers to share and
collaborate on a wide range of supplier relationship and demand chain processes
(the "eCAS Software") upon the terms and subject to the conditions of this
Agreement;

         WHEREAS, the Purchaser and AI Research Corporation entered into a
Letter of Intent dated April 27, 2001 (the "Letter of Intent"), summarizing the
material terms and conditions of the acquisition of the eCAS Software by
Purchaser, which Letter of Intent shall be superceded by this Agreement; and

         WHEREAS, Sellers desire to sell to Purchaser, and Purchaser desires to
purchase from Sellers, the eCAS Software in accordance with the terms and
conditions set forth in this Agreement.

         NOW, THEREFORE, the parties hereby agree as follow in consideration of
the mutual premises and covenants contained herein:

                                    ARTICLE I

                      Purchase and Sale of Acquired Assets

                  SECTION 1.01.  Purchase and Sale.


         (a)      On the terms and subject to the conditions of this Agreement,
Sellers shall sell, assign, transfer, convey and deliver to Purchaser, and
Purchaser shall purchase from Sellers all of the right, title and interest as of
the Closing (as defined in Section 2.01) of Sellers in, to and under the
Acquired Assets (as defined in Section 1.02(a)), for (i) an aggregate purchase
price of $200,000 in cash (the "Purchase Price"), $25,000 of which Purchaser has
paid pursuant to the terms of the Letter of Intent, and $175,000 of which is
payable as set forth in Section 2.02; and (ii) the issuance of a warrant to
purchase 125,000 shares of common stock of the Purchaser (the "Warrant") having
an exercise price of $1.00 per share and exercisable for a three-year period
from the date hereof and in the form attached hereto as Exhibit A. The purchase
and sale of the Acquired Assets is referred to in this Agreement as the
"Acquisition".

                  SECTION 1.02.  Acquired Assets and Excluded Assets.

         (a)      The term "Acquired Assets" means all the properties, assets,
goodwill and rights of whatever kind and nature, real or personal, tangible or
intangible, that are owned, leased or licensed by Sellers as of the date hereof
(the "Closing Date") and used, held for use or intended to be used primarily in
the operation of the eCAS Software, including:

                  (i)      all work-in-progress relating to the eCAS Software,
         including all drafts, notes, customer feedback and related research
         materials;
<PAGE>   5
                  (ii)     all patents (including all reissues, divisions,
         continuations and extensions thereof), patent applications, patent
         rights, trademarks, trademark registrations, whether or not issued or
         issuable, trademark applications, servicemarks, whether or not issued
         or issuable, service mark applications, trade names, business names,
         brand names including any such rights related to the eCAS Software,
         copyrights including any such rights related to the eCAS Software
         (including any extension thereof), rights to file such extensions or
         reversions therein, copyright registrations (including applications
         therefor or rights to apply therefor), designs, design registrations
         (including applications therefor or rights to apply therefor), and all
         rights to any of the foregoing including the names "eCAS", "LinkSpan",
         "eOrder", "eSalesForce", "eConnect", "eMessaging", "eSupply",
         "eBizRule", "eAnalysis", "CastaLink" and "CastaLink.com", and any
         domain (including Internet domain names), trademarks, servicemarks and
         any other personal or property rights associated with such names and
         all source code documentation and user manuals related to the eCAS
         Software ("Intellectual Property");

                  (iii)    all trade secrets, confidential information,
         inventions, know-how, formulae, processes, procedures, research
         records, records of inventions, test information, user manuals,
         installation guides, implementation guides (including templates),
         training materials, maintenance and technical support materials and
         related databases, websites (including, without limitation, any domain
         name associated with such websites and any and all graphical and
         textual material appearing on such websites), market surveys and
         marketing know-how relating to the eCAS Software (the "Technology");
         and

                  (iv)     all equipment listed on Schedule 1.02(a) holding the
         source code and object code for all, including the latest, versions of
         the eCAS Software currently available or in development.

         (b)      The term "Excluded Assets" means all assets not identified in
Section 1.02(a), and all rights of Sellers under this Agreement and the other
agreements and instruments executed and delivered in connection with this
Agreement (the "Ancillary Agreements").

                  SECTION 1.03.  Excluded Liabilities.


         (a)      Notwithstanding any other provision of this Agreement or any
Ancillary Agreement, and regardless of any disclosure to Purchaser, Purchaser
shall not assume any Excluded Liability, each of which shall be retained and
paid, performed and discharged when due by Sellers, or CastaLink as applicable.
The term "Excluded Liability" means:

                  (i)      any liability, obligation or commitment of CastaLink
         or Sellers, including, without limitation for Taxes (as defined in
         Section 3.08), relating to or arising out of the operation of the eCAS
         Software or ownership of any Acquired Asset, whether express or
         implied, liquidated, absolute, accrued, contingent or otherwise, or
         known or unknown, and based upon, arising out of or resulting from any
         fact, circumstance, occurrence, condition, act or omission existing on
         or occurring on or prior to the Closing, or arising primarily out of
         the operation or conduct by CastaLink or Sellers or any of their
         respective affiliates of any business other than that related to the
         eCAS Software or ownership of any Excluded Asset; and

                  (ii)     any liability, obligation or commitment of CastaLink
         or Sellers (A) arising out of any actual or alleged breach by CastaLink
         or Sellers of, or nonperformance by CastaLink or Sellers under, any
         contracts, licenses, agreements, commitments and all other legally
         binding arrangements, whether oral or written, ("Contract") or (B)
         arising under any Contract, including any Contract either (x) required
         to be listed in Schedule 3.05 and not so listed or (y) entered into in
         violation of this Agreement.

         (b)      Purchaser shall acquire the Acquired Assets free and clear of
         any and all liabilities, obligations, licenses and commitments, and
         free and clear of all Liens (as defined in Section 3.04).

                  SECTION 1.04.  Consents of Third Parties.



                                       2
<PAGE>   6
                  If for any reason, Purchaser or Sellers determine that the
consent of a third party to the sale and transfer of the Acquired Assets
hereunder is necessary and such consent is not obtained prior to the Closing,
Sellers and Purchaser shall cooperate (at Sellers' own expense) in any lawful
and reasonable arrangement reasonably proposed by Purchaser and Sellers to
obtain such consent, or to treat any such asset hereunder as an Excluded Asset.

                  SECTION 1.05.  "As Is" Condition.

                  Except as expressly set forth in this Agreement, the Acquired
Assets hereunder are conveyed to and accepted by Purchaser in an "AS IS"
condition, free of any warranties or representations whatsoever, and SELLERS
EXPRESSLY DISCLAIM ANY AND ALL OTHER EXPRESS OR IMPLIED WARRANTIES WITH RESPECT
THERETO, INCLUDING BUT NOT LIMITED THE WARRANTY OF MERCHANTABILITY AND WARRANTY
OF FITNESS FOR A PARTICULAR PURPOSE.

                                   ARTICLE II

                                   The Closing

                  SECTION 2.01. Closing Date. The closing of the Acquisition
(the "Closing") shall take place at the offices of Hogan & Hartson L.L.P., 1800
Broadway, Suite 200, Boulder, Colorado 80302, or at other such mutually
agreeable location, June 1, 2001 at 12:00 p.m. PDT on the date hereof (the
"Closing Date").

                  SECTION 2.02. Transactions To Be Effected at the Closing. At
the Closing:

         (a)      Sellers shall deliver to Purchaser (i) such appropriately
executed bills of sale, assignments, consents and other instruments of transfer
relating to the Acquired Assets in form and substance reasonably satisfactory to
Purchaser and its counsel, (ii) such documents to be delivered by Sellers in
accordance with the terms of Section 6.01, (iii) such other documents as
Purchaser or its counsel may reasonably request to demonstrate satisfaction of
the conditions and compliance with the covenants set forth in this Agreement,
(iv) on one or more fully functional and operational development systems, all
programs, systems, data, materials, Intellectual Property, Technology or other
property in whatever form developed or in development by or for, or purchased or
licensed by, CastaLink or Sellers necessary to, or useful in, the day to day
maintenance, administration and operation of eCAS Software (the "eCAS Backup").
The eCAS Backup shall include all source (human-readable) and object
(machine-readable or executable) code, in whatever form, for all, including the
latest, versions of the eCAS Software currently available or in development and
any and all related documentation (including documentation relating to software
development, software architecture, quality testing, marketing, training,
support, implementation, customer feedback, websites and marketing alliances ),
databases (including native or proprietary format databases and, in the case of
any relational databases, ASCII or plain text representations of the data
elements thereof), database queries or scripts used in the creation or dynamic
generation of website pages, graphical and design elements, user information and
passwords; and (v) one computer system on which all current and prior versions
of the eCAS Software are installed, and certification that to the best of
Sellers' knowledge that no current and prior versions of the eCAS Software are
installed on any other computer systems; and

         (b)      Purchaser shall deliver to Sellers, pursuant to Schedule
2.02(b), (i) payment, by wire transfer to two bank accounts designated in
writing by Sellers, in immediately available funds in an aggregate amount equal
to $175,000 and as provided in Schedule 2.02 (b) (ii) such documents to be
delivered by Purchaser in accordance with the terms of Section 6.02, (iii) a
fully executed Warrant, and (iv) such other documents as Sellers or their
counsel may reasonably request to demonstrate satisfaction of the conditions and
compliance with the obligations set forth in this Agreement.



                                       3
<PAGE>   7
                                   ARTICLE III

                    Representations and Warranties of Sellers

                  Each Seller severally and not jointly represents and warrants
to Purchaser as of the date hereof as follows:

                  SECTION 3.01. Organization, Standing and Power. Each Seller is
duly organized, validly existing and in good standing under the laws of the
state of its incorporation or formation and has full corporate power and
authority and possesses all governmental franchises, licenses, permits,
authorizations and approvals necessary to enable it to own, lease or otherwise
hold its properties and assets, including the Acquired Assets, and to conduct
its other businesses as presently conducted, other than such franchises,
licenses, permits, authorizations and approvals the lack of which, individually
or in the aggregate, have not had and could not reasonably be expected to have a
material adverse effect on the business, assets, condition (financial or
otherwise), prospects or results of operations of Sellers or of the eCAS
Software, or on the ability of each Seller to perform its obligations under this
Agreement and the Ancillary Agreements or to consummate the Acquisition and the
other transactions contemplated hereby (a "Seller Material Adverse Effect"). For
the purposes of this Agreement, the term "Use" or "Used" means the use,
operation, development marketing, distribution or sale of the eCAS Software.
Each Seller has delivered to Purchaser true and complete copies of its articles
of incorporation or partnership agreement, as amended through the date of this
Agreement.

                  SECTION 3.02. Authority; Execution and Delivery;
Enforceability. Each Seller has full power and authority to execute this
Agreement and the Ancillary Agreements to which it is a party and to consummate
the Acquisition and the other transactions contemplated hereby and thereby. The
execution and delivery by each Seller of this Agreement and the Ancillary
Agreements to which it is a party and the consummation by each Seller of the
Acquisition and the other transactions contemplated hereby and thereby have been
duly authorized by all necessary corporate action, including any required vote
or approval by the shareholders or partners of Sellers. Each Seller has duly
executed and delivered this Agreement and each Ancillary Agreement to which it
is a party, and this Agreement and each Ancillary Agreement to which it is, a
party constitute, its legal, valid and binding obligation, enforceable against
it in accordance with its terms, except as subject to laws of general
application relating to bankruptcy, insolvency and relief of debtors and rules
of law governing specific performance, injunctive relief or other equitable
remedies.

                  SECTION 3.03. No Conflicts; Consents. The execution and
delivery by Sellers of this Agreement and the Ancillary Agreements do not, and
the consummation of the Acquisition and the other transactions contemplated
hereby and thereby and compliance by Sellers with the terms hereof and thereof
will not: (a) conflict with, or result in any violation of its organization
documents; (b) result in the creation of any Lien upon the Acquired Assets. No
consent, approval, license, permit, order or authorization ("Consent") of, or
registration, declaration or filing with, any Federal, state, local or foreign
government or any court of competent jurisdiction, administrative agency or
commission or other governmental authority or instrumentality, domestic or
foreign (a "Governmental Entity"), is required to be obtained or made by or with
respect to a Seller in connection with (A) the execution, delivery and
performance of this Agreement or any Ancillary Agreement or the consummation of
the Acquisition or the other transactions contemplated hereby and thereby or (B)
the Use of the eCAS Software by Purchaser following the Closing as Used on the
date hereof.

                  SECTION 3.04. Assets Other than Intellectual Property,
Technology, Software and Internet Domain Names.


         (a)      Sellers have good and valid title to all the Acquired Assets,
in each case free and clear of all mortgages, liens, security interests,
charges, easements, leases, subleases, covenants, rights of way, options,
claims, restrictions or encumbrances of any kind (collectively, "Liens").

         (b)      This Section 3.04 does not relate to Intellectual Property,
Technology, the eCAS Software and Internet Domain Names (as defined in Section
3.05(f)), such items being the subject of Section 3.05.

                                       4
<PAGE>   8
                  SECTION 3.05. Intellectual Property; Technology; Internet
Domain Names; Software.


         (a)      Schedule 3.05 sets forth a true and complete list of all
Intellectual Property, owned, used, filed by or licensed to Sellers and used,
held for use or intended to be used primarily in the operation of the eCAS
Software, other than unregistered designs and copyrights that, individually and
in the aggregate, are not material to the Use of the eCAS Software as presently
Used. With respect to all Intellectual Property that is registered or subject to
an application for registration, Schedule 3.05 sets forth a list of all
jurisdictions in which such Intellectual Property is registered or registrations
applied for and all registration and application numbers. Except as set forth in
Schedule 3.05, (i) all the Intellectual Property has been duly registered in,
filed in or issued by the appropriate Governmental Entity where such
registration, filing or issuance is necessary or appropriate for the Use of the
eCAS Software as presently Used, (ii) Sellers are the sole and exclusive owner
of, and Sellers have the right to use, execute, reproduce, display, perform,
modify, enhance, distribute, prepare derivative works of and sublicense, without
payment to any other person, all the Intellectual Property and the consummation
of the Acquisition and the other transactions contemplated hereby does not and
will not conflict with, alter or impair any such rights, and (iii) neither
CastaLink nor Sellers have received any written or oral communication from any
person asserting any ownership interest in any Intellectual Property.

         (b)      Neither CastaLink nor Sellers have granted any license of any
kind relating to any Technology or Intellectual Property or the marketing or
distribution thereof except as set forth in Schedule 3.05.
Neither CastaLink nor Sellers are bound by or a party to any option, license or
similar Contract relating to the Intellectual Property of any other person for
the use of such Intellectual Property in the Use of the eCAS Software, except as
set forth in Schedule 3.05. The Use of the eCAS Software as presently Used does
not violate, conflict with or infringe upon the Intellectual Property of any
other person. There are no claims pending or, to the knowledge of CastaLink or
Sellers, threatened, against CastaLink or Sellers by any person with respect to
the ownership, validity, enforceability, effectiveness or use of the eCAS
Software and any Intellectual Property and neither CastaLink nor Sellers or
their respective affiliates have received any written or oral communication
alleging that CastaLink, Sellers or any of their respective affiliates have in
the Use of the eCAS Software violated any rights relating to Intellectual
Property of any person.

         (c)      All material Technology has been maintained in confidence in
accordance with protection procedures customarily used in the industry to
protect rights of like importance. All former and current members of management
and key personnel of CastaLink, including all former and current employees,
agents, consultants and independent contractors who have contributed to or
participated in the conception and development of material Technology
(collectively, "Personnel"), have executed and delivered to CastaLink a
proprietary information agreement restricting such person's right to disclose
proprietary information of CastaLink and its affiliates. All former and current
Personnel either (i) have been party to a "work-for-hire" arrangement or
agreement with CastaLink, in accordance with all Applicable Laws, that has
accorded CastaLink full, effective, exclusive and original ownership of all
tangible and intangible property thereby arising, including but not limited to
the Technology and the Intellectual Property, or (ii) have executed appropriate
instruments of assignment ("Invention Assignment Agreements") in favor of
CastaLink as assignee that have conveyed to CastaLink full, effective and
exclusive ownership of all tangible and intangible property thereby arising,
including but not limited to the Technology and the Intellectual Property. No
former or current Personnel have asserted a claim against CastaLink or Sellers
in connection with such person's involvement in the conception and development
of any Technology and no such claim has been threatened. To the knowledge of
Sellers, none of the current officers and employees of CastaLink has any patents
issued or applications pending for any device, process, design or invention of
any kind now used in the eCAS Software, which patents or applications have not
been assigned to CastaLink and Sellers, with such assignment duly recorded in
the United States Patent and Trademark Office.

         (d)      Sellers are the sole and exclusive owner of, and Sellers have
the right to use, without payment to any other person, the Acquired Assets.

         (e)      The eCAS Software and any other computer software held for use
or intended to be used in the operation of the eCAS Software, other than
off-the-shelf commercial software programs and databases which, individually,
cost less than $1,000, are listed on Schedule 3.05. To the knowledge of
CastaLink and Sellers, (x) none of the eCAS Software and no use thereof,
infringes upon or violates any patent, copyright, trade secret or other
proprietary right of any other person and (y) no claim with respect to any such
infringement or violation is




                                       5
<PAGE>   9
threatened. CastaLink and Sellers have taken all steps reasonably necessary to
protect their right, title and interest in and to the eCAS Software, including
the use of written agreements containing appropriate confidentiality provisions
with all third parties having access to the source code relating to the eCAS
Software, except where the failure to have such agreements, individually or in
the aggregate, could not reasonably be expected to have a Seller Material
Adverse Effect.

                  Sellers possess or have access to the original and all copies
of all documentation, including all source code for the eCAS Software. Sellers
own all the eCAS Software, free and clear of all Liens.

                  Any programs, modifications, enhancements or other inventions,
improvements, discoveries, methods or works of authorship included in the eCAS
Software that were created by employees of CastaLink were made in the regular
course of such employees' employment with CastaLink using CastaLink's facilities
and resources and, as such, constitute "works made for hire".

         (f)      Schedule 3.05 sets forth a true and complete list of all
Internet domain names and applications therefor ("Internet Domain Names")
registered to CastaLink or used by CastaLink in connection with eCAS Software.
Sellers have the exclusive right to use, without payment to any other party, all
Internet Domain Names, including the Internet Domain Name "CastaLink.com", that
have been registered to CastaLink. All Internet Domain Names have been duly
registered with or issued by the appropriate authority, whether governmental or
private, and all necessary maintenance fees have been paid to continue all such
rights in effect. To the knowledge of CastaLink and Sellers, no claims have been
asserted by any person with respect to the registration, validity or use of any
such Internet Domain Names, or challenging or questioning the validity or
enforceability of the registration contracts relating thereto, in any
jurisdiction, domestic or foreign. To the knowledge of CastaLink and Sellers,
the registration of the Internet Domain Names listed in Schedule 3.05 is not in
violation of any "cyber squatting" laws in any jurisdiction, domestic or
foreign.

                  SECTION 3.06.  Contracts.

         (a)      Except as set forth in Schedule 3.06, CastaLink is not a party
to or bound by any Contract related to the eCAS Software or its Use. Complete
and correct copies of all Contracts listed in the Schedule 3.06, together with
all modifications and amendments thereto, have been made available to Purchaser.

         (b)      To the knowledge of Sellers, CastaLink has performed all
obligations required to be performed by it to date under the Contracts, and it
is not (with or without the lapse of time or the giving of notice, or both) in
breach or default in any material respect thereunder and, to the knowledge
Sellers, no other party to any Contract is (with or without the lapse of time or
the giving of notice, or both) in breach or default in any material respect
thereunder. The Application License Agreement between CastaLink and Rod-L
Electronics dated January 31, 2001 and the letter agreement between CastaLink
and Khong Guan Corporation dated December 28, 1999 (the "Customer Contracts")
shall terminate on or prior to the Closing Date and Sellers shall certify to
Purchaser on the Closing Date that such Customer Contracts have been so
terminated in accordance with Section 6.01(c) herein.

                  SECTION 3.07. Sufficiency of Acquired Assets. The Acquired
Assets (together with the Excluded Assets specified in Section 1.02(b)),
comprise all the assets employed in connection with the eCAS Software. The
Acquired Assets are sufficient for the Use of the eCAS Software immediately
following the Closing in substantially the same manner as currently Used.


                                       6
<PAGE>   10
                  SECTION 3.08.  Taxes.

         (a)      For purposes of this Agreement:

                  "Tax" means (i) any tax, governmental fee or other like
assessment or charge of any kind whatsoever (including any tax imposed under
Subtitle A of the Code and any net income, alternative or add-on minimum tax,
gross income, gross receipts, sales, use, ad valorem, value added, transfer,
franchise, profits, license, withholding tax on amounts paid, payroll,
employment, excise, severance, stamp, capital stock, occupation, property,
environmental or windfall profit tax, premium, custom, duty or other tax),
together with any interest, penalty, addition to tax or additional amount due,
imposed by any Governmental Entity (domestic or foreign) responsible for the
imposition of any such tax (a "Taxing Authority"), (ii) any liability for the
payment of any amount of the type described in clause (i) above as a result of a
party to this Agreement being a member of an affiliated, consolidated or
combined group with any other corporation at any time on or prior to the Closing
Date and (iii) any liability of any person with respect to the payment of any
amounts of the type described in clause (i) or (ii) above as a result of any
express or implied obligation of such person to indemnify any other person.

                  "Code" means the Internal Revenue Code of 1986, as amended.

         (b)      CastaLink and each Seller, and any affiliated group, within
the meaning of Section 1504 of the Code, of which CastaLink or a Seller is or
has been a member, has filed or caused to be filed in a timely manner (within
any applicable extension periods) all material Tax returns, reports and forms
required to be filed by it and all such returns, reports and forms are true,
complete and correct, all Taxes due have been timely paid in full or will be
timely paid in full by the due date thereof, and no Tax Liens exist with respect
to the Acquired Assets and no audits or claims are being conducted or asserted
with respect to any Taxes.

         (c)      Each Seller has prepared, executed and filed all returns,
questionnaires, applications or other documents regarding any Transfer Tax that
is required to be filed by Sellers prior to Closing.

                  SECTION 3.09. Proceedings. There is no pending or, to the
knowledge of Sellers, threatened Proceeding, arising out of the Use of the eCAS
Software or against any Acquired Asset and that relates to the transactions
contemplated by this Agreement. There is not any Proceeding or claim by
CastaLink or Sellers pending, or which CastaLink or Sellers intend to initiate
against any other Person. To the knowledge of Sellers, neither CastaLink nor
Sellers are a party or subject to or in default under any Judgment applicable to
the Use of the eCAS Software or any Acquired Asset nor is there any pending or
threatened investigation of or affecting any Acquired Asset.

                  SECTION 3.10. Compliance with Applicable Laws. To the
knowledge of Sellers, the eCAS Software, and Sellers' Use of the eCAS Software,
is in compliance with all Applicable Laws, including those relating to
occupational health and safety. Neither CastaLink nor Sellers have received any
written or oral communication from any person that alleges that it, the eCAS
Software or its Use of the eCAS Software is not in compliance in any material
respect with any Applicable Law. This Section 3.10 does not relate to matters
with respect to Taxes, which are the subject of Section 3.08.

                  SECTION 3.11. Disclosure. No representation or warranty of
Sellers contained in this Agreement or in any Ancillary Agreement, and no
statement contained in any document, certificate or Schedule furnished or to be
furnished by or on behalf of Sellers to Purchaser or any of their respective
representatives pursuant to this Agreement, contains or will contain any untrue
statement of a material fact, or omits or will omit to state any material fact
necessary, in light of the circumstances under which it was or will be made, in
order to make the statements herein or therein not misleading or necessary in
order to fully and fairly provide the information required to be provided in any
such document, certificate or Schedule.


                                       7
<PAGE>   11
                                   ARTICLE IV

                   Representations and Warranties of Purchaser

                  Purchaser hereby represents and warrants to Sellers as of the
date hereof as follows:

                  SECTION 4.01. Organization, Standing and Power. Purchaser is
duly organized, validly existing and in good standing under the laws of the
State of Delaware and has full corporate power and authority and possesses all
governmental franchises, licenses, permits, authorizations and approvals
necessary to enable it to own, lease or otherwise hold its properties and assets
and to carry on its business as presently conducted, other than such franchises,
licenses, permits, authorizations and approvals the lack of which, individually
or in the aggregate, have not had and could not reasonably be expected to have a
material adverse effect on the ability of Purchaser to consummate the
Acquisition and the other transactions contemplated hereby (a "Purchaser
Material Adverse Effect").

                  SECTION 4.02. Authority; Execution and Delivery; and
Enforceability. Purchaser has full power and authority to execute this Agreement
and the Ancillary Agreements to which it is, or is specified to be, a party and
to consummate the Acquisition and the other transactions contemplated hereby and
thereby. The execution and delivery by Purchaser of this Agreement and the
Ancillary Agreements to which it is, or is specified to be, a party and the
consummation by Purchaser of the Acquisition and the other transactions
contemplated hereby and thereby have been duly authorized by all necessary
corporate action. Purchaser has duly executed and delivered this Agreement and
prior to the Closing will have duly executed and delivered each Ancillary
Agreement to which it is, or is specified to be, a party, and this Agreement
constitutes, and each Ancillary Agreement to which it is, or is specified to be,
a party will after the Closing constitute, its legal, valid and binding
obligation, enforceable against it in accordance with its terms.

                  SECTION 4.03. No Conflicts; Consents. The execution and
delivery by Purchaser of this Agreement do not, the execution and delivery by
Purchaser of each Ancillary Agreement to which it is, or is specified to be, a
party will not, and the consummation of the Acquisition and the other
transactions contemplated hereby and thereby and compliance by Purchaser with
the terms hereof and thereof will not conflict with, or result in any violation
of or default (with or without notice or lapse of time, or both) under, or give
rise to a right of termination, cancellation or acceleration of any obligation
or loss of a material benefit under, or result in the creation of any Lien upon
any of the properties or assets of Purchaser under, any provision of (i)
Certificate of Incorporation or by-laws of Purchaser, (ii) any Contract to which
Purchaser is a party or by which any of its properties or assets is bound or
(iii) any Judgment or Applicable Law applicable to Purchaser or its properties
or assets. No Consent of or registration, declaration or filing with any
Governmental Entity is required to be obtained or made by or with respect to
Purchaser or any of its subsidiaries in connection with the execution, delivery
and performance of this Agreement or any Ancillary Agreement or the consummation
of the Acquisition or the other transactions contemplated hereby and thereby.


                                       8
<PAGE>   12
                                    ARTICLE V

                                    Covenants

                  SECTION 5.01. Confidentiality. Sellers shall keep
confidential, and cause their respective affiliates, officers, directors,
partners, employees and advisors to keep confidential, all information relating
to the eCAS Software or its Use, except as required by law or administrative
process and except for information that is available to the public on the
Closing Date, or thereafter becomes available to the public other than as a
result of a breach of this Section 5.01. The covenant set forth in this Section
5.01 shall terminate one year after the Closing Date; provided however, this
termination provision shall not apply to the release of the existence and the
terms and conditions of this Agreement. Sellers may release such information
only upon the express written approval of Purchaser.

                  SECTION 5.02. Best Efforts. Each party shall, and shall cause
its affiliates to, use its best efforts (at its own expense) to obtain, and to
cooperate in obtaining, all Consents from third parties necessary or appropriate
to permit the transfer of the Acquired Assets to Purchaser to the extent that
such consents shall not have been obtained by the Closing Date; provided,
however, that the parties shall not be required to pay or commit to pay any
amount to (or incur any obligation in favor of) any person from whom any such
consent may be required (other than nominal filing or application fees).

                  SECTION 5.03.  Expenses; Transfer Taxes.

                           (a)      Except as set forth in Sections 5.03(b),
5.05 and 8.03 and Article VII, all costs and expenses incurred in connection
with this Agreement and the Ancillary Agreements and the transactions
contemplated hereby and thereby shall be paid by the party incurring such
expense, including all costs and expenses incurred pursuant to Sections 1.04 and
5.02.

                           (b)      All Transfer Taxes applicable to the
conveyance and transfer from Sellers to Purchaser of the Acquired Assets and any
other transfer or documentary Taxes or any filing or recording fees applicable
to such conveyance and transfer shall be paid by Sellers. Each party shall use
reasonable efforts to avail itself of any available exemptions from any such
Taxes or fees, and to cooperate with the other parties in providing any
information and documentation that may be necessary to obtain such exemptions.

                  SECTION 5.04. Brokers or Finders. Each of Purchaser and
Sellers represent, as to itself and its affiliates, that no agent, broker,
investment banker or other firm or person is or will be entitled to any broker's
or finder's fee or any other commission or similar fee in connection with any of
the transactions contemplated by this Agreement.

                  SECTION 5.05.  Post-Closing Cooperation.

                           (a)      Purchaser and Sellers shall cooperate with
each other, and shall cause their officers to cooperate with each other, (at
Sellers' expense) for a period of sixty (60) days for an amount of time not to
exceed twenty (20) hours during such period after the Closing to ensure the
orderly transition of the eCAS Software from Sellers to Purchaser.

                           (b)      If Purchaser requests that CastaLink's
previous employees provide additional technical, development or marketing
assistance following the Closing, Purchasers agree to negotiate in good faith
the scope of such services and an hourly consulting fee payable by Purchaser to
CastaLink's previous employees for such services.


                                       9
<PAGE>   13
                  SECTION 5.06. Publicity. No public release or announcement
concerning the transactions contemplated hereby shall be issued by any party
without the prior consent of the other parties (which consent shall not be
unreasonably withheld).


                  SECTION 5.07. Further Assurances. From time to time, as and
when requested by any party, each party shall execute and deliver, or cause to
be executed and delivered, all such documents and instruments and shall take, or
cause to be taken, all such further or other actions (subject to Section 5.02),
as such other party may reasonably deem necessary to consummate the transactions
contemplated by this Agreement, including, in the case of Sellers, executing and
delivering to Purchaser such assignments, deeds, bills of sale, consents and
other instruments as Purchaser or its counsel may reasonably request as
necessary for such purpose.

                  SECTION 5.08. Names and Internet Domain Names Following
Closing.


         (a)      Immediately following the Closing, Sellers shall amend or
terminate any certificate of assumed name or d/b/a filings so as to eliminate
its right to use the names LinkSpan, eCAS, eOrder, eSalesForce, eConnect,
eBizRule, eMessaging, eAnalysis and eSupply, or any name that, in the judgment
of Purchaser, is similar to any such names, and Sellers shall not thereafter use
those names or other names acquired by Purchaser hereunder or names confusingly
similar thereto. Purchaser agrees not to use the name "CastaLink" or
"CastaLink.com" as a corporate name or d/b/a designation in the State of
California. Sellers agree not to use the name "CastaLink" or "CastaLink.com" in
connection with the sale of goods or services that directly or indirectly
compete with the eCAS Software or in a manner that would be reasonably likely to
result in confusion among customers or clients of the eCAS Software from
Purchaser.

         (b)      Immediately following the Closing, Sellers shall not use the
Internet Domain Name CastaLink.com, or any domain name that, in the judgement of
Purchaser, is similar to any such name and Sellers shall execute an assignment
of Internet Domain Names in a form mutually acceptable to Sellers and Purchaser.

                                   ARTICLE VI

                        Actions and Deliveries at Closing

                  SECTION 6.01. Sellers' Actions and Deliveries at Closing.


         (a)      Sellers' Officer's Certificate. Each Seller shall deliver to
Purchaser a certificate signed by an authorized officer of Seller to the effect
that: (i) the representations and warranties of Seller in this Agreement and the
Ancillary Agreements are true and correct in all material respects as of the
Closing Date, except to the extent such representations and warranties expressly
relate to an earlier date (in which case such representations and warranties are
true and correct in all material respects, on and as of such earlier date), in
each case except for breaches as to matters that, individually or in the
aggregate, could not reasonably be expected to have a Seller Material Adverse
Effect; and

                  (ii) Seller has performed or complied in all material respects
with all obligations and covenants required by this Agreement to be performed or
complied with by Seller by the time of the Closing.

         (b)      Transfer Taxes. Sellers shall deliver to Purchaser copies of
all returns, questionnaires, applications or other documents regarding any
Transfer Tax that Sellers have proposed, executed and filed prior to Closing.


         (c)      Notice of Termination. Sellers shall deliver to Purchaser all
notices of termination of the Customer Contracts obtained in accordance with
Section 3.06.

         (e)      Technology Assignments. Sellers shall deliver to Purchaser
appropriate instruments of assignment in favor of CastaLink as assignee from all
Personnel that have not been party to a "work-for-hire" arrangement or agreement
with CastaLink that has accorded CastaLink full, effective, exclusive and
original


                                       10
<PAGE>   14
ownership of all tangible and intangible property thereby arising,
conveying to CastaLink, effective and exclusive ownership of all tangible and
intangible property thereby arising. Sellers shall further deliver to Purchaser
all appropriate instruments of assignment in favor of Sellers as assignee from
CastaLink transferring all right, title and interest in and to the eCAS
Software, the Technology and the Intellectual Property pursuant to the terms of
the Security Agreement.

         (f)      Other Documents. Sellers shall furnish to Purchaser such other
documents relating to Sellers' corporate existence and authority (including
copies of resolutions of the respective boards of directors or partners of
Sellers), absence of Liens, and such other matters as Purchaser or its counsel
may reasonably request prior to the Closing Date.

         (g)      eCAS Software. Purchaser shall have tested the eCAS Software
prior to Closing and shall have determined to its satisfaction that it has the
ability to operate the eCAS Software in a form substantially identical to that
in which it operated as of the date of the Letter of Intent to the exclusion of
any other person.

                  SECTION 6.02. Purchaser's Actions and Deliveries at Closing.

         (a)      Purchaser Officer's Certificate. Sellers shall have received a
certificate signed by an authorized officer of Purchaser to the effect that:

                  (i)      the representations and warranties of Purchaser made
in this Agreement and the Ancillary Agreement shall be true and correct in all
material respects as of the Closing Date, except to the extent such
representations and warranties expressly relate to an earlier date (in which
case such representations and warranties shall be true and correct in all
material respects, on and as of such earlier date), in each case except for
breaches as to matters that, individually or in the aggregate, could not
reasonably be expected to have a Purchaser Material Adverse Effect; and

                  (ii)     Purchaser shall have performed or complied in all
material respects with all obligations and covenants required by this Agreement
to be performed or complied with by Purchaser by the time of the Closing.

         (b)      Transfer Taxes. Purchaser shall have prepared, executed and
filed all returns, questionnaires, applications or other documents regarding any
Transfer Tax that is required to be filed by Purchaser prior to Closing.

                  SECTION 6.03 Amendments and Waivers. This Agreement may not be
amended except by an instrument in writing signed on behalf of each of the
parties hereto. By an instrument in writing Purchaser, on the one hand, and
Sellers, on the other hand, may waive compliance by the other party with any
term or provision of this Agreement that such other party was or is obligated to
comply with or perform.

                                   ARTICLE VII

                                 Indemnification

                  SECTION 7.01. Indemnification by Sellers. Sellers shall
jointly and severally indemnify Purchaser and its affiliates and each of their
respective officers, directors, employees, stockholders, agents and
representatives against, and hold them harmless from, any loss, liability,
claim, damage or expense (including reasonable legal fees and expenses)
("Losses"), as incurred (payable promptly upon written request), arising from,
in connection with or otherwise with respect to:

                  (i)      any breach of any representation or warranty of
                           Sellers that survives the Closing and is contained in
                           this Agreement, in any Ancillary Agreement or in any
                           other document delivered in connection herewith or
                           therewith;


                                       11
<PAGE>   15
                  (ii)     any breach of any obligation or covenant of Sellers
                           contained in this Agreement or in any Ancillary
                           Agreement;

                  (iii)    any Excluded Liability; and

                  (iv)     any fees, expenses or other payments incurred or owed
                           by Sellers to any brokers, financial advisors or
                           comparable other persons retained or employed by it
                           in connection with the transactions contemplated by
                           this Agreement.

                  SECTION 7.02. Indemnification by Purchaser. Purchaser shall
indemnify Sellers, their affiliates and each of their respective officers,
directors, employees, stockholders, partners, agents and representatives
against, and agrees to hold them harmless from, any Loss, as incurred (payable
promptly upon written request), arising from, in connection with or otherwise
with respect to (i) any breach of any representation or warranty of Purchaser
contained in this Agreement, in any Ancillary Agreement or in any other document
delivered in connection herewith, (ii) any breach of any obligation or covenant
of Purchaser contained in this Agreement or in any Ancillary Agreement, or (iii)
any fees, expenses or other payments incurred or owed by Purchaser to any
brokers, financial advisors or other comparable persons retained or employed by
it in connection with the transactions contemplated by this Agreement or by any
Ancillary Agreement.

                  SECTION 7.03. Termination of Indemnification. The obligations
to indemnify and hold harmless any party, pursuant to Sections 7.01(i) and (iii)
or 7.02(i) and (iii), shall terminate one year from the date hereof, except with
respect to breaches of the representations and warranties set forth in Sections
3.04 (title) and 3.08 (taxes) and claims for fraud by an intentional
misrepresentation, with respect to which the indemnification obligations shall
continue until the expiration of the applicable statute of limitations and (ii)
the covenants and agreements in this Agreement and the Ancillary Agreements
shall survive except to the extent that they are specifically limited by their
terms; provided, however, that such obligations to indemnify and hold harmless
shall not terminate with respect to any item as to which the person to be
indemnified shall have, before the expiration of the applicable period,
previously made a claim by delivering a notice of such claim pursuant to Section
7.04 to the party to be providing the indemnification. Notwithstanding anything
to the contrary contained herein or in any Ancillary Agreement, in no event
shall the amount of liability of Sellers or Purchaser for breach of any
representation, warranty, indemnity or covenant or otherwise under, or arising
in connection with, this Agreement or any Ancillary Agreement exceed $200,000;
provided, however, that in addition to the indemnification obligations set forth
in this paragraph, in the event the amount of such indemnification claim exceeds
$200,000, but not by more than $75,000, then (A) if the Warrant has not been
exercised, the Warrant shall be terminated; or (B) if the Warrant has been
exercised, Purchaser shall have the right to repurchase from Sellers that number
of shares of the Common Stock issued to Sellers upon exercise of the Warrant at
a purchase price equal to the market price (but in no event less than $1.00 per
share as adjusted for stock splits, combinations and the like) that is equal to
the amount of such indemnification claim in excess of $200,000 but in no event
by more than $75,000 such that Seller's maximum liability for indemnification
for breach of any representation, warranty, indemnity or covenant or otherwise
under, or arising in connection with, this Agreement or any Ancillary Agreement
shall not exceed $275,000. The Sellers' obligation to indemnify and hold
Purchaser harmless for breach of any representation, warranty, indemnity or
covenant or otherwise under, or arising in connection with, this Agreement or
any Ancillary Agreement shall immediately terminate upon the closing of a merger
or reorganization of Purchaser with or into any other entity (unless Purchaser's
stockholders of record as constituted immediately prior to such transaction or
sale will, immediately after such transaction or sale hold at least 50% of the
voting power of the surviving or acquiring entity or its parent) or a sale of
all or substantially all of the assets of the Purchaser.

                  SECTION 7.04. Procedures.


         (a)      Third Party Claims. In order for a party (the "indemnified
party"), to be entitled to any indemnification provided for under this Agreement
in respect of, arising out of or involving a claim made by any person against
the indemnified party (a "Third Party Claim"), such indemnified party must
notify the indemnifying party in writing of the Third Party Claim promptly
following receipt by such indemnified party of written notice of


                                       12
<PAGE>   16
the Third Party Claim; provided, however, that failure to give such notification
shall not affect the indemnification provided hereunder except to the extent the
indemnifying party shall have been actually and materially prejudiced as a
result of such failure. Thereafter, the indemnified party shall deliver to the
indemnifying party, promptly following the indemnified party's receipt thereof,
copies of all notices and documents (including court papers) received by the
indemnified party relating to the Third Party Claim.

         (b)      Assumption. If a Third Party Claim is made against an
indemnified party, the indemnifying party shall be entitled to participate in
the defense thereof and, if it so chooses, to assume the defense thereof with
counsel selected by the indemnifying party; provided, however, that such counsel
is reasonably satisfactory to by the indemnified party. Should the indemnifying
party so elect to assume the defense of a Third Party Claim, the indemnifying
party shall not be liable to the indemnified party for any legal expenses
subsequently incurred by the indemnified party in connection with the defense
thereof. If the indemnifying party assumes such defense, the indemnified party
shall have the right to participate in the defense thereof and to employ
counsel, at its own expense, separate from the counsel employed by the
indemnifying party, it being understood that the indemnifying party shall
control such defense. The indemnifying party shall be liable for the fees and
expenses of counsel employed by the indemnified party for any period during
which the indemnifying party has not assumed the defense thereof. If the
indemnifying party chooses to defend or prosecute a Third Party Claim, all the
indemnified parties shall cooperate in the defense or prosecution thereof.
Whether or not the indemnifying party assumes the defense of a Third Party
Claim, the indemnified party shall not admit any liability with respect to, or
settle, compromise or discharge, such Third Party Claim without the indemnifying
party's prior written consent (which consent shall not be unreasonably
withheld).

         (c)      Other Claims. In the event any indemnified party should have a
claim against any indemnifying party under Section 7.01 or 7.02 that does not
involve a Third Party Claim being asserted against or sought to be collected
from such indemnified party, the indemnified party shall deliver notice of such
claim with reasonable promptness to the indemnifying party. Subject to Section
7.03, the failure by any indemnified party so to notify the indemnifying party
shall not relieve the indemnifying party from any liability that it may have to
such indemnified party under Section 7.01 or 7.02, except to the extent that the
indemnifying party demonstrates that it has been materially prejudiced by such
failure. If the indemnifying party does not notify the indemnified party within
30 calendar days following its receipt of such notice that the indemnifying
party disputes its liability to the indemnified party under Section 7.01 or
7.02, such claim specified by the indemnified party in such notice shall, in the
absence of manifest error, be conclusively deemed a liability of the
indemnifying party and the indemnifying party shall pay the amount of such
liability to the indemnified party on demand or, in the case of any notice in
which the amount of the claim (or any portion thereof) is estimated, on such
later date when the amount of such claim (or such portion thereof) becomes
finally determined.

                  SECTION 7.05. Survival of Representations. The
representations, warranties, covenants and agreements contained in this
Agreement and in any document delivered in connection herewith shall survive the
Closing solely for purposes of Article VII and shall terminate as set forth in
Section 7.03.

                                  ARTICLE VIII

                               General Provisions

                  SECTION 8.01. Assignment. This Agreement and the rights and
obligations hereunder shall not be assignable or transferable by Purchaser or
Sellers (including by operation of law in connection with a merger or
consolidation of Purchaser or Sellers) without the prior written consent of the
other parties hereto. Any attempted assignment in violation of this Section 8.01
shall be void.

                  SECTION 8.02. No Third-Party Beneficiaries. Except as provided
in Article VIII, this Agreement is for the sole benefit of the parties hereto
and their permitted assigns and nothing herein expressed or implied shall give
or be construed to give to any person, other than the parties hereto and such
assigns, any legal or equitable rights hereunder.


                                       13
<PAGE>   17
                  SECTION 8.03. Attorney Fees. A party in breach of this
Agreement shall, on demand, indemnify and hold harmless the other party for and
against all reasonable out-of-pocket expenses, including legal fees, incurred by
such other party by reason of the enforcement and protection of its rights under
this Agreement. The payment of such expenses is in addition to any other relief
to which such other party may be entitled.

                  SECTION 8.04. Notices. All notices or other communications
required or permitted to be given hereunder shall be in writing and shall be
delivered by hand or sent by facsimile or sent, postage prepaid, by registered,
certified or express mail or reputable overnight courier service and shall be
deemed given when so delivered by hand or facsimile, or if mailed, three days
after mailing (one business day in the case of express mail or overnight courier
service), as follows:

                  1.       if to Purchaser,

                           PlanetCad Inc.
                           2520 55th Street
                           Boulder, CO  80301
                           (303) 209-9100
                           (303) 209-9200 (facsimile)
                           Attention:  Doug Hughes

                           with a copy to:

                           Hogan & Hartson
                           One Tabor Center, Suite 1500
                           1200 Seventeenth Street
                           Denver, CO  80202
                           (303) 899-7300
                           (303) 899-7333 (facsimile)
                           Attention:  Whitney Holmes, Esq.

                           if to Sellers,

                           Capstone Ventures SBIC, L.P.
                           3000 Sand Hill Road
                           Building 1, Suite 290
                           Menlo Park, CA  94025
                           (650) 854-2523
                           (650) 854-9010 (facsimile)
                           Attention: Gene Fischer

                           AI Research Corporation
                           4191 Briarwood Way
                           Palo Alto, CA
                           (650) 852-9140
                           (650) 852-9522 (facsimile)
                           Attention:  Richard L. Leza

                           with a copy to:

                           Wilson Sonsini Goodrich & Rosati
                           650 Page Mill Road
                           Palo Alto, CA  94304-1050
                           (650) 565-3650
                           (650) 493-6811 (facsimile)
                           Attention:  Mark Casper


                                       14
<PAGE>   18
                  SECTION 8.05. Interpretation; Exhibits and Schedules; Certain
Definitions.


         (a)      The headings contained in this Agreement, in any Exhibit or
Schedule hereto and in the table of contents to this Agreement are for reference
purposes only and shall not affect in any way the meaning or interpretation of
this Agreement. All Exhibits and Schedules annexed hereto or referred to herein
are hereby incorporated in and made a part of this Agreement as if set forth in
full herein. Any capitalized terms used in any Schedule or Exhibit but not
otherwise defined therein, shall have the meaning as defined in this Agreement.
When a reference is made in this Agreement to a Section, Exhibit or Schedule,
such reference shall be to a Section of, or an Exhibit or Schedule to, this
Agreement unless otherwise indicated.

         (b)      For all purposes hereof:

                  "affiliate" of any person means another person that directly
or indirectly, through one or more intermediaries, controls, is controlled by,
or is under common control with, such first person.

                  "including" means including, without limitation. "person"
means any individual, firm, corporation, partnership, limited liability company,
trust, joint venture, Governmental Entity or other entity.

                  "subsidiary" of any person means another person, an amount of
the voting securities, other voting ownership or voting partnership interests of
which is sufficient to elect at least a majority of its Board of Directors or
other governing body (or, if there are no such voting interests, 50% or more of
the equity interests of which) is owned directly or indirectly by such first
person or by another subsidiary of such person.

                  SECTION 8.06. Counterparts. This Agreement may be executed in
one or more counterparts, all of which shall be considered one and the same
agreement, and shall become effective when one or more such counterparts have
been signed by each of the parties and delivered to the other party.

                  SECTION 8.07. Entire Agreement. This Agreement and the
Ancillary Agreements, along with the Schedules and Exhibits thereto, contain the
entire agreement and understanding between the parties hereto with respect to
the subject matter hereof and supersede all prior agreements and understandings
relating to such subject matter. Neither party shall be liable or bound to any
other party in any manner by any representations, warranties or covenants
relating to such subject matter except as specifically set forth herein or in
the Ancillary Agreements.

                  SECTION 8.08. Severability. If any provision of this Agreement
(or any portion thereof) or the application of any such provision (or any
portion thereof) to any person or circumstance shall be held invalid, illegal or
unenforceable in any respect by a court of competent jurisdiction, such
invalidity, illegality or unenforceability shall not affect any other provision
hereof (or the remaining portion thereof) or the application of such provision
to any other persons or circumstances.

                  SECTION 8.09. Governing Law. This Agreement shall be governed
by and construed in accordance with the internal laws of the State of Colorado
applicable to agreements made and to be performed entirely within such State,
without regard to the conflicts of law principles of such State.

                  SECTION 8.10. Dispute Resolution. Sellers and Purchaser agree
to mandatory arbitration proceedings for resolution of all the disputes relating
to the Agreement, the Ancillary Agreements and any other agreements delivered
pursuant hereto or thereto under the applicable Rules of the American
Arbitration Association (U.S. disputes), and judgment upon the award rendered in
the arbitration proceeding may be entered in any court having jurisdiction
thereof. The arbitration shall be held in Boulder, Colorado, or at another
location if it can be selected by mutual agreement. The arbitration award may
grant a reimbursement to the prevailing party of all of its fees and expenses,
including reasonable attorneys' fees. Without waiving any right to arbitration
under this Agreement, any party may apply to any court having jurisdiction
hereof and seek injunctive relief so as to maintain


                                       15
<PAGE>   19
the status quo until such time as the arbitration award is rendered or the
controversy is resolved. No party nor the arbitrator(s) may disclose the
existence, content, or results of any arbitration proceeding hereunder without
the prior written consent of both parties.

                            [Signature page follows]



                                       16
<PAGE>   20
                  IN WITNESS WHEREOF, Sellers and Purchaser have duly executed
this Asset Purchase Agreement as of the date first written above.

                 SELLERS:

                 CAPSTONE VENTURES SBIC, L.P., a Delaware limited partnership


                 By: Capstone SBIC Management, Inc.

                          By: /s/ Eugene J. Fischer
                              ----------------------------------------
                          Its: President
                               ---------------------------------------

                 AI RESEARCH CORP., a California corporation

                 By:      /s/ Richard L. Leza
                     -------------------------------------------------
                        Richard L. Leza, CEO/Chairman

                 PURCHASER:

                 PLANETCAD INC., a Delaware corporation

                 By:      /s/ Jim Bracking
                     -------------------------------------------------
                        Jim Bracking, CEO/President



                                       17