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                                                                   EXHIBIT 10.28

                                  CONFIDENTIAL

                           CHANGE IN CONTROL AGREEMENT

     This Agreement is between PlanetCAD Inc., a Delaware corporation
("Company"), and David Hushbeck (the "Executive"), and shall be effective as of
November __, 2001 (the "Effective Date").

     WHEREAS the Company wishes to assure itself of the continuity of the
Executive's services in the event of any actual or threatened change in control
of the Company;

     WHEREAS the Company and the Executive accordingly desire to enter into this
Agreement on the terms and conditions set forth below;

     NOW, THEREFORE, in consideration of the promises and mutual covenants set
forth herein and other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties agree as follows:

     1.  TERM OF AGREEMENT. The term of this Agreement (the "Term") shall
commence on the Effective Date and shall continue until the first anniversary
thereof; provided, however, that on such anniversary date and on each subsequent
anniversary of the Effective Date, the term of this Agreement may be extended
for one additional year in the sole discretion of the board of directors of the
Company (the "Board") upon written notice to the Executive; and provided
further, that if an actual or threatened Change in Control (as defined in
paragraph 3 below) shall have occurred during the original or any extended Term
of this Agreement, then the Term of this Agreement shall continue for a period
of 12 calendar months beyond the calendar month in which such actual or
threatened Change in Control occurs.

     2.  EMPLOYMENT AFTER CHANGE IN CONTROL. If the Executive is in the employ
of the Company on the date of an actual or threatened Change in Control, the
Company shall continue Executive in its employ for the period commencing on the
date of the actual or threatened Change in Control and ending on the last day of
the Term of this Agreement (the "Employment Period"). During the Employment
Period, the Executive shall hold such position with the Company and exercise
such authority and perform such duties as are substantially commensurate with
the Executive's position, authority and duties immediately prior to the actual
or threatened Change in Control. The Executive agrees that, during the
Employment Period, the Executive shall devote his full professional time and
attention to the Executive's duties and perform such duties faithfully and
efficiently; provided, however, that nothing in this Agreement shall prevent the
Executive from voluntarily resigning from employment upon 15 days' written
notice to the Company under circumstances which do not constitute a Termination
(as defined in paragraph 5 below).

     3.  CHANGE IN CONTROL. For purposes of this Agreement, an actual "Change in
Control" means the occurrence of any of the following:

         a.  the stockholders of the Company approve a definitive agreement to
merge the Company into or consolidate the Company with another entity, sell or
otherwise

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dispose of all or substantially all of its assets, or adopt a plan of
liquidation. However, a Change in Control shall not be deemed to have occurred
by reason of a transaction (or a substantially concurrent or otherwise related
series of transactions) (a "Transaction") upon the completion of which seventy
percent (70%) or more of the beneficial ownership of the voting power of the
Company, the surviving corporation or corporation directly or indirectly
controlling the Company or the surviving corporation, as the case may be, is
held by the same persons (although not necessarily in the same proportion) as
held the beneficial ownership of the voting power of the Company immediately
prior to the Transaction (except that upon the completion thereof, employees or
employee benefit plans of the Company may be a new holder of such beneficial
ownership). A transaction with an "Affiliate" of the Company (as defined in Rule
12b-2 under the Securities Exchange Act of 1934, as amended (the "Exchange
Act")) shall not be treated as a Change in Control; or

         b.  the "beneficial ownership" (as defined in Rule 13(d)(3) under the
Exchange Act) of securities representing thirty percent (30%) or more of the
combined voting power of the Company is acquired, other than from the Company,
by any "person" as defined in Sections 13(d) and 14(d) of the Exchange Act
(other than by any member of the Board or other fiduciary holding securities
under an employee benefit plan or other similar stock plan of the Company).

     For the purposes of this Agreement, a "threatened Change in Control" means
(i) the determination by the Board, in the exercise of its reasonable business
judgment, that a third person has taken steps to effect an actual Change in
Control and that such actual Change of Control could occur within 120 days after
such determination, or (ii) the Company has entered into a definitive agreement
with any third person that, upon the consummation of the transactions
contemplated thereby, will result in an actual Change in Control.

     4.  COMPENSATION DURING THE EMPLOYMENT PERIOD. During the Employment
Period, the Executive shall be compensated as follows:

         a.  The Executive shall receive an annual salary which is not less than
his annual salary immediately prior to the Employment Period;

         b.  the Executive shall be eligible to participate in short-term and
long-term cash-based incentive compensation plans which, in the aggregate,
provide bonus opportunities that are not materially less favorable to the
Executive than the opportunities provided to the Company's other executives with
similar responsibilities and performance levels;

         c.  the Executive shall be eligible to participate in stock option,
performance awards, restricted stock and other equity-based incentive
compensation plans (the "Plans") on a basis not materially less favorable to the
Executive than the greater of the Plans available (i) to the Executive
immediately prior to the Employment Period, or (ii) to other executives of the
Company with similar responsibilities and performance and cash compensation
levels; and

         d.  the Executive shall be eligible to receive employee benefits
(including, but not limited to, tax-qualified and nonqualified savings plan
benefits, medical insurance, disability income protection, life insurance
coverage and death benefits) and perquisites which are not materially less
favorable to the Executive than (i) the employee benefits and perquisites
provided to the Company's other executives, or (ii) the employee benefits,
excluding the

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Company's required matching contribution, if any, to the Executive's 401(k) plan
if the Company terminates its policy of making such matching contributions to
its employees during the Employment Period, and perquisites to which the
Executive would be entitled under the Company's employee benefit plans and
perquisites as in effect immediately prior to the Employment Period.

     5.  TERMINATION. For purposes of this Agreement, "Termination" shall mean
termination of the employment of the Executive during the Employment Period (i)
by the Company, for any reason other than death or Cause (as described below),
or (ii) by resignation of the Executive upon the occurrence of one of the
following events:

         a.  a material change in the nature or scope of the Executive's
position, authority or duties, a breach of any of the subparagraphs of paragraph
4 above, or the material breach by the Company of any other provision of this
Agreement;

         b.  the relocation of the Executive's office to a location more than 50
miles from the location of the Executive's office immediately prior to the
Employment Period;

         c.  the failure of the Company to obtain a satisfactory agreement from
any successor to assume and agree to perform this Agreement, as contemplated in
paragraph 11(d), below.

     The date of the Executive's Termination under this paragraph 5 shall be the
date specified by the Executive or the Company, as the case may be, in a written
notice to the other party complying with the requirements of paragraph 11(a)
below. For purposes of this Agreement, "Cause" means, in the reasonable judgment
of the Board, (i) the willful and continued failure by the Executive to
substantially perform all of the Executive's duties with the Company, after
written notification by the Company of such failure, (ii) the willful engaging
by the Executive in conduct which is demonstrably injurious to the Company,
monetarily or otherwise, or (iii) the engaging by Executive in egregious
misconduct involving serious moral turpitude. For purposes of this Agreement, no
act, or failure to act, on the Executive's part shall be deemed "willful" unless
done, or omitted to be done, by the Executive not in good faith and without
reasonable belief that such action was in the best interest of the Company.

     6.  SEVERANCE PAYMENTS. In the event of a Termination described in
paragraph 5 above:

         a.  the Company shall pay the Executive's unpaid salary, accrued
vacation pay and unreimbursed business expenses through and including the date
of Termination; and

         b.  in addition, following Executive's execution of a legal release in
a form satisfactory to Company in its sole discretion and drafted so as to
ensure a final, complete and enforceable release of all claims (excluding claims
for indemnification pursuant to Article XI of the Company's bylaws, as amended
from time to time) that Executive has or may have against Company relating to or
arising in any way from Executive's employment with Company and/or the
termination thereof, and complete and continuing confidentiality of Company's
proprietary information and trade secrets, the circumstances of Executive's
separation from Company, and compensation received by Executive in connection
with that separation, in lieu of the amount otherwise payable under paragraph 4
above, the Company

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shall reimburse Executive for all costs associated with the continuation of
Executive's coverage, to the extent of Executive's coverage immediately prior to
the date of Termination and to the extent equivalent amounts are paid by the
Company immediately prior to the date of Termination, under the Company's group
medical insurance policy, under COBRA for the first 6 months following the date
of Termination or until Executive becomes eligible for comparable benefits under
benefit plans sponsored by another employer, and shall also be entitled to:

              (1)  a lump sum payment in cash no later than ten (10) business
days after the date of Termination equal to four months of the Executive's
annual salary rate in effect immediately prior to the date of Termination;

              (2)  immediate vesting of that portion of the Executive's
outstanding stock options as of the date of Termination equal to the sum of one
eighth plus the product of one forty-eighth multiplied by the number of whole
months the Executive has been employed by the Company through the date of
Termination; and

              (3)  an extension of the exercise period of such fully vested
stock options to 30 months following the date of Termination.

     7.  DEDUCTIONS AND WITHHOLDING. All payments to the Executive under this
Agreement will be subject to applicable deductions and withholding of state and
federal taxes.

     8.  CONFIDENTIALITY, NON-SOLICITATION AND NON-COMPETITION. The Executive
agrees that:

         a.  Except as may be required by the lawful order of a court or agency
of competent jurisdiction, or except to the extent that the Executive has the
express written authorization from the Company, the Executive agrees to keep
secret and confidential for a period of one year following the termination of
Executive's employment all non-public information concerning the Company or any
entity in which the Company has a 25% or greater ownership interest
("Company-Related Entity") which was acquired by or disclosed to Executive
during the course of Executive's employment with the Company or any
Company-Related Entity controlled by the Company, and not to disclose the same,
either directly or indirectly, to any other person, firm or business entity or
to use it in any way.

         b.  While the Executive is employed by the Company or any Company-
Related Entity and for a period of one year after the date the Executive's
employment terminates for any reason, the Executive covenants and agrees that
Executive will not, whether for Executive or for any other person, business,
partnership, association, firm, company or corporation, initiate contact with,
solicit, divert or take away any of the customers (entities or individuals from
which the Company or any Company-Related Entity receives rents or payments for
services) of the Company or any Company-Related Entity or employees of the
Company or any Company-Related Entity in existence from time to time during
Executive's employment with the Company or any Company-Related Entity and at the
time of such initiation, solicitation or diversion.

         c.  While the Executive is employed by the Company or any Company-
Related Entity and for a period of one year after the date the Executive's
employment terminates for any reason, the Executive covenants and agrees that
Executive will not, directly or indirectly, engage in, assist, perform services
for, plan for, establish or open, or have any

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financial interest (other than (i) ownership of 1% or less of the outstanding
stock of any corporation listed on the New York or American Stock Exchange or
included in the National Association of Securities Dealers Automated Quotation
System, or (ii) ownership of securities in any entity affiliated with the
Company) in any person, firm, corporation, or business entity (whether as an
employee, officer, director or consultant) that engages in the operations,
development, management or financing of any business that is competitive with
the Company's business at the time of such termination, including the Company's
supply chain manufacturing software business and its enterprise solutions
business.

     9.  DISPUTE RESOLUTION; JURISDICTION; SERVICE OF PROCESS.

         a.  Executive and Company agree that in the event of any controversy or
claim arising out of this Agreement, they shall negotiate in good faith to
resolve the controversy or claim privately, amicably and confidentially. Each
party may consult with counsel in connection with such negotiations.

         b.  Executive and the Company agree and consent to be subject to the
exclusive jurisdiction of any state or federal court sitting in Denver,
Colorado, in any action or proceeding arising out of or relating to this
Agreement and agrees that all claims in respect of the action or proceeding may
be heard and determined in any such court. Executive and the Company also agree
not to bring any action or proceeding arising out of or relating to this
Agreement in any other court. Each of the Executive and the Company waives any
defense of inconvenient forum to the maintenance of any action or proceeding so
brought and waives any bond, surety, or other security that might be required of
any other party with respect thereto. Each of the Executive and the Company
agrees that a final judgment in any action or proceeding so brought shall be
conclusive and may be enforced by suit on the judgment or in any other manner
provided by law or at equity.

         c.  Each party hereby irrevocably consents to the service of any and
all process in any such suit, action or proceeding by the delivery of such
process to such party at the address and in the manner provided in subparagraph
11(a) below. Nothing in this subparagraph 9(c), however, shall affect the right
of any Party to serve legal process in any other manner permitted by law or at
equity.

     10. MITIGATION AND SET-OFF. The Executive shall not be required to mitigate
the amount of any payment provided for in this Agreement by seeking other
employment or otherwise. The Company shall not be entitled to set-off against
the amounts payable to the Executive under this Agreement any amounts earned, or
which could have been earned, by the Executive after the date of Termination of
Executive's employment with the Company.

     11. MISCELLANEOUS PROVISIONS.

         a.  NOTICE. Except as otherwise provided herein, either the Company or
the Executive may terminate the employment relationship upon no less than
fifteen (15) days' notice to the other party. Except as otherwise specifically
provided in this Agreement, any notices, requests, demands or other
communications provided for by this Agreement shall be sufficient if in writing
and if sent by telecopy or facsimile transmission or by hand delivery or
registered, certified, or overnight mail to the Executive at the last address
Executive has filed in writing with the Company or, in the case of the Company,
to the attention of the Secretary of the Company, at its principal executive
offices. Such notices and communications shall be

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deemed to have been received on the date of confirmation of receipt, in the case
of telecopy or facsimile transmission, or upon the date of delivery thereof or
the fifth (5th) business day after the mailing thereof, whichever is earlier, in
the case of the remaining delivery methods.

         b.  BINDING EFFECT; ASSIGNMENT. This Agreement shall inure to the
benefit of, and shall be binding upon, the parties hereto and their respective
successors, assigns, heirs, and legal representatives. This Agreement may not be
assigned by Executive, nor may Executive assign or pledge any of his rights,
including rights to payment, hereunder.

         c.  GOVERNING LAW. The provisions of this Agreement shall be construed
in accordance with the substantive laws of the State of Colorado, without
application of conflict of laws provisions thereunder.

         d.  SUCCESSORS TO THE COMPANY. The Company shall require any successor,
whether direct or indirect, by purchase, merger, consolidation or otherwise, and
whether to all or substantially all of the business and/or assets of the
Company, to assume the obligations of this Agreement. Such assumption shall be
by an express agreement signed by both the successor Company and the Executive
and shall be reasonably satisfactory to the Executive. If the Company fails to
obtain such an express assumption, that shall be a breach of this Agreement and
shall entitle the Executive to the same benefits and compensation as he would be
entitled to if the Employment Period was terminated under paragraph 5.

         e.  EMPLOYMENT STATUS. Nothing in this Agreement shall be deemed to
create an employment agreement between the Company and the Executive providing
for the employment of the Executive by the Company for any fixed period of time,
other than as provided in paragraphs 1 and 2. The Executive's employment is
terminable at-will by the Company or the Executive, meaning that either party
may terminate the employment relationship at any time, with or without cause,
subject to the provisions of paragraphs 1, 2, and 5. Upon termination of the
Executive's employment prior to the date of a threatened Change in Control,
there shall be no further rights under this Agreement.

         f.  ENTIRE AGREEMENT. This Agreement contains the entire agreement
between the parties hereto and supersedes all prior agreements and
understandings, oral or written, between the parties hereto concerning its
subject matter.

         g.  AMENDMENTS AND WAIVERS. This Agreement may not be modified or
amended except by an instrument or instruments in writing signed by the party
against whom enforcement or any such modification or amendment is sought. Either
party hereto may, by an instrument in writing, waive compliance by the other
party with any term or provision of this Agreement on the part of such other
party hereto to be performed or complied with. The waiver by any party hereto of
a breach of any term or provision of this Agreement shall not be construed as a
waiver of any subsequent breach.

         h.  CONSTRUCTION. Headings in this Agreement are for convenience of
reference only and shall not control the meaning of this Agreement. Whenever
applicable, masculine and neutral pronouns shall equally apply to the feminine
genders; the singular shall include the plural and the plural shall include the
singular. The parties have reviewed and understand this Agreement, and each has
had a full opportunity to negotiate the Agreement's terms and to consult with
counsel of their own choosing. Therefore, the parties expressly

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waive all applicable common law and statutory rules of construction that any
provision of this Agreement should be construed against the Agreement's drafter,
and agree that this Agreement and all amendments thereto shall be construed as a
whole, according to the fair meaning of the language used.

         i.  SEVERABILITY. In the event that any provision or portion of this
Agreement shall be determined to be invalid or unenforceable for any reason, the
remaining provisions of this Agreement shall be unaffected thereby and shall
remain in full force and effect.

         j.  COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original, but all of which
together shall constitute one and the same agreement.

     IN WITNESS WHEREOF, the Executive has hereunto set his hand and, pursuant
to the authorization from its Board of Directors, the Company has caused these
presents to be executed in its name and on its behalf, all as of the day and
year first above written.

PLANETCAD INC.:                                      DAVID HUSHBECK

By:    /s/ Eugene J. Fischer                               /s/ David Hushbeck
   -------------------------------                   ---------------------------
Name:  Eugene J. Fischer                             David Hushbeck
     -----------------------------
Title: Chairman
      ----------------------------

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