<PAGE>

                                  Exhibit 4.3
                                  -----------

                        DESIGN AUTOMATION SYSTEMS, INC.
                            SHAREHOLDERS' AGREEMENT

     THIS SHAREHOLDERS' AGREEMENT (this "Agreement"), is entered into as of
February 18, 2000 by and among DESIGN AUTOMATION SYSTEMS, INC., d/b/a EpicEdge,
a Texas corporation (the "Company"); Carl Rose, Charles Leaver, Jeff Sexton and
Kelly Knake (together, the "Principal Shareholders"); Edgewater Private Equity
Fund III, L.P., a Delaware limited partnership ("Edgewater"), Aspen Finance
Investors I, LLC, a Colorado limited liability company ("Aspen"), Fleck T.I.M.E.
Fund, LP, a Connecticut limited partnership ("TIME"), Fleck Family Partnership
II, LP, a Florida limited partnership ("Fleck Family"), LJH Partners LP, a
Delaware limited partnership ("LJH"), Wain Investment, LLC, an Ohio limited
liability company ("Wain"), Gerald C. Allen, an individual ("Allen"), and John
Paul DiJoria, an individual ("DiJoria"; together with Edgewater, Aspen, TIME,
Fleck Family, LJH, Wain and Allen are sometimes collectively referred to herein
as the "Investors" and individually as an "Investor") (the Principal
Shareholders, the Investors and each person who assumes the obligations of a
Shareholder pursuant to Section 2.4 hereof are each individually referred to
herein as a "Shareholder" and are collectively referred to herein as the
"Shareholders").

                             W I T N E S S E T H:

     WHEREAS, the Investors together own of record or beneficially 2,260,000 of
the issued and outstanding shares of common stock, $.01 par value, of the
Company (the "Common Stock"), and the Principal Shareholders in the aggregate
own of record or beneficially 11,835,660 shares of Common Stock as follows: Carl
Rose, 9,389,650 shares; Charles Leaver, 1,432,310 shares; Jeff Sexton, 300,000
shares; and Kelly Knake, 713,700 shares; and

     WHEREAS, the parties hereto consider it to be in the best interests of the
Company, its business and of the Shareholders that the provisions of this
Agreement will determine various matters relating to the Common Stock owned by
the Shareholders.

     NOW, THEREFORE, in consideration of the mutual promises, covenants and
conditions herein contained, and for other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, the parties hereto
covenant and agree as follows:

                                   ARTICLE I
                           VOTING, MANAGEMENT, ETC.

     1.1   Voting. The Company's Articles of Incorporation provides that the
           ------
Common Stock shall entitle the holders thereof to one (1) vote per share on each
proposition submitted to

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shareholders of the Company for their vote thereon.

     1.2  Control Agreements. It is agreed that the Principal Shareholders shall
          ------------------
(i) vote their shares of Common Stock and take all actions within their
authority necessary for the Company to comply with the provisions of Section
1.2(a)(i) hereof and Section 6.3 of that certain Stock Purchase Agreement of
even date herewith between the Company and the Investors (the "Purchase
Agreement") and take all necessary action to effectuate such provisions,
including without limitation, the increase in the size of and the election of
certain new members to the Board (as hereinafter defined) as required by Section
1.2(a)(i) hereof and Section 6.3 of the Purchase Agreement; and (ii)
collectively and severally vote the respective shares held by each for the
election of the Investor Representative or the Investor Representatives (as such
terms are defined herein), as Board members of the Company and shall undertake
or cause to be undertaken any and all of the actions within their authority
necessary in whatever capacity, including, without limitation, an amendment to
the Articles of Incorporation and By-Laws of the Company, if such action is
required, whether as a director, shareholder, officer or employee, so as to
provide for all the events described in Section 1.2(a)(i) hereof and Section 6.3
of the Purchase Agreement and for the following provisions:

     (a)  Directors.

          (i)    Designation of Directors. As soon as practicable but in no
event later than April 15, 2000, the Board of Directors of the Company (the
"Board") shall consist of seven (7) directors, and one (1) of whom shall be
designated by the Majority Holders (as such term is defined in the Purchase
Agreement) (the "Investors Representative"); provided, however, that in the
event the Investors own of record or beneficially less than 500,000 shares in
the aggregate of Investor Common Stock, such director slot shall no longer be
designated by the Investors. Upon the occurrence of an Event of Default (as
defined in the Purchase Agreement), the number of directors shall be increased
to eight (8) and two (2) directors shall be designated by the Majority Holders
(the "Investors Representatives"). The Investor Representative or Investors
Representatives, as the case may be, shall be a person reasonably satisfactory
to the Company. The Company hereby acknowledges and agrees that Aaron Fleck,
James Gordon, Bob Allison and/or Brian Thompson are acceptable Investors
Representatives.

          (ii)   Expenses. Each director will be reimbursed at each meeting of
the Board for his reasonable out-of-pocket expenses in attending such meeting
including a reasonable mileage allowance.

          (iii)  Meetings. The Board shall meet no less frequently than
quarterly.

          (iv)   Indemnification. The Company shall at all times maintain
directors and officers insurance coverage covering the Investors
Representative(s) and provide for indemnification of all of the directors and
officers under its Bylaws and by agreement satisfactory to the Investors.

                                       2
<PAGE>

     (b)  Compensation Committee. The Board shall have a compensation committee
authorized and elected pursuant to applicable Bylaws and resolutions. Such
committee shall vote on, and approve by majority vote, the compensation of all
officers and key employees, except that the Chief Executive Officer shall not
vote on his compensation.

     1.3  Stock Option Plan. It is understood and agreed among the parties
          -----------------
hereto that (i) the Board will continue to maintain a Stock Option Plan (the
"Stock Option Plan") pursuant to which the Board may from time to time grant
stock options to purchase Common Stock to employees, directors and consultants
of the Company, (ii) such issuances under the Stock Option Plan may constitute
up to fifteen percent (15%) of the issued and outstanding shares of Common Stock
on a fully diluted basis (and such shares of Common Stock have been reserved for
issuance under the Stock Option Plan), and (iii) such issuances will have a
dilutive impact on all shareholders of the Company. Any issuance of options
under the Stock Option Plan to any employees, directors and consultants of the
Company shall require the approval of the aforesaid Board or compensation
committee thereof.

                                  ARTICLE II
                        RESTRICTIONS ON STOCK TRANSFERS

     2.1  Applicable Definitions. For purposes of the provisions of this
          ----------------------
Agreement, the following definitions shall be applicable:

     (a)  "Investor Common Stock" means the Common Stock owned by the Investors.

     (b)  "Permitted Transferee" means a Transferee of Principal Common Stock in
a Permitted Transfer.

     (c)  "Permitted Transfers" means (i) the sale of up to 125,000 shares
Principal Common Stock in the aggregate owned by Carl Rose; and (ii) the sale of
up to 50,000 shares of Principal Common Stock in the aggregate owned by each
Jeff Sexton, Charles Leaver and Kelly Knake.

     (d)  "Principal Common Stock" means the Common Stock owned by the Principal
Shareholders.

     (e)  "Shares" shall include and refer to all Common Stock owned by the
Shareholders, individually and collectively.

     (f)  "Transfer" shall include a sale, transfer, or any other act whereby a
Shareholder's rights of ownership are sold, transferred, disposed of pledged,
hypothecated, encumbered, or in any way impaired or affected.

     (g)  "Transferee" shall mean a person to whom a Shareholder proposes to
Transfer Shares or to whom Shares have been transferred.

                                       3
<PAGE>

     2.2  Restrictions on Sale of Shares by a Principal Shareholder. Except for
Permitted Transfers, no Principal Shareholder shall Transfer any Shares until
thirty (30) days after a registration statement with respect to the resale of
all of the Investor Common Stock, upon such terms and provisions as set forth in
that certain Registration Agreement of even date herewith between the Company
and the Investors (the "Registration Agreement"), becomes effective.

                                  ARTICLE III
          REPRESENTATIONS, WARRANTIES AND AGREEMENTS OF SHAREHOLDERS

     This Agreement is being entered into by the Company and each Shareholder in
reliance upon the following representations, covenants and warranties
respectively made by the Shareholders in favor of the Company and the
Shareholders.

     3.1  Authorization. Each Shareholder represents and warrants that (a) this
          -------------
Agreement, when executed and delivered by him, her or it, will constitute a
valid, legally binding and enforceable obligation of such Shareholder; and (b)
such Shareholder is not prevented by any legal requirement or agreement from
entering into this Agreement and performing such Shareholder's obligations
hereunder. The fulfillment of and compliance with the terms of this Agreement by
such Shareholder will not (i) conflict with or result in a breach of the terms,
conditions or provisions of, (ii) constitute a default under, or (iii) result in
a violation of, breach of or default under (a) any Shareholders' partnership
agreement (as applicable) or (b) any law, statute, rule or regulation to which
you are subject, or (c) any agreement, instrument, order, judgment or decree to
which such Shareholder is a party, bound or subject.

     3.2  Sophistication, Financial Strength, Access, Etc. Each Shareholder
          -----------------------------------------------
represents, warrants and acknowledges that, with respect to the Company, he, she
or it is an Accredited Investor (as that term is defined in Rule 501 promulgated
by the Securities and Exchange Commission under the Act), that he, she or it has
such knowledge and experience in business and financial matters as to be capable
of evaluating the merits and risks of the investment contemplated to be made
hereunder; that such investment bears a high degree of risk and could result in
a total loss of his, his or its investment; and that he, she or it have
sufficient financial strength to hold the same as an investment and to bear the
economic risks of such investment (including possible loss of such investment)
for an indefinite period of time.

     3.3  No Broker or Finder. Each Shareholder represents and warrants that he,
          -------------------
she or it has not engaged any broker or finder in connection with this Agreement
or the transactions contemplated hereby, except as set forth in the Purchase
Agreement.

     3.4  Reiteration and Survival of Representations and Warranties. The
          ----------------------------------------------------------
representations and warranties of each Shareholder contained in this Article III
shall be true on and as of the date of this Agreement and shall survive the
completion of the transactions contemplated hereby.

                                  ARTICLE IV
                                   TRANSFER

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     4.1  Legend on Share Certificates. All Share certificates issued to the
          ----------------------------
Principal Shareholders, shall have imprinted thereon a legend (in addition to
any applicable securities law legend to be contained on the Share certificates
issued to the Investors and the Principal Shareholders) substantially to the
following effect: "The sale, transfer or other disposition or pledge or other
encumbrance of shares represented by this Certificate is subject to a
Shareholders Agreement dated February 18, 2000 (the "Agreement"), among Design
Automation Systems, Inc. a Texas corporation d/b/a EpicEdge (the "Company"), the
Shareholder named on this Certificate and certain other parties named in the
Agreement, which Agreement includes certain restrictions on transfer and certain
options to purchase or sell the shares represented by this Certificate. A copy
of the Agreement is on file in the office of the Secretary of the Company and
may be reviewed by application thereto. Each holder hereof shall be bound by all
provisions of the Agreement." All Shares in the hands of persons or entities who
are parties to this Agreement and all Shares acquired by the Company or by
anyone else from parties to this Agreement or from the heirs, executors,
administrators, legal or personal representatives, successors or assigns of
parties to this Agreement by direct or indirect conveyance pursuant to the terms
hereof, shall be subject to all of the provisions contained in this Agreement
and to all of the restrictions on, and provisions relating to, voluntary or
involuntary sale, transfer or other dispositions of, and options to purchase or
sell, such Shares.

     4.2  Private Offer; Transfer. Each Investor understands and agrees that:
          -----------------------

     (a)  the Investor Common Stock may not be sold, transferred or otherwise
disposed of without registration under the Act or an exemption therefrom and
that in the absence of an effective registration statement covering the Investor
Common Stock or an available exemption from registration under the Act, the
Investor Common Stock must be held indefinitely. In particular, each Shareholder
is aware that the Investor Common Stock may not be sold pursuant to Rule 144
promulgated under the Act unless all of the conditions of that Rule 144 are met.
Each Investor represents that, in the absence of an effective registration
statement covering the Investor Common Stock, such Investor will sell, transfer
or otherwise dispose of the Investor Common Stock only (a) in accordance with
Section 2.3 hereof and (b) in a manner consistent with its representations and
warranties set forth herein and then only in accordance with the provisions of
Section 4.3 hereof; and (b) in no event will such Investor make a transfer or
disposition of any of the Investor Common Stock other than pursuant to an
effective registration statement under the Act, unless and until (i) the
Investor shall have notified the Company and shall have furnished the Company
with a statement of the circumstances surrounding the disposition, and (ii) if
applicable, the Investor shall have complied with the provisions of Article II
hereof.

     4.3  Notice of Proposed Transfer. If, prior to any transfer or sale of any
          ---------------------------
Investor Common Stock, the Investor desiring to effect such transfer or sale
shall deliver a written notice to the Company describing briefly the manner of
such transfer or sale and a written opinion of counsel for such Shareholder
(provided that such counsel, and the form and substance of such opinion, are
reasonably satisfactory to the Company) to the effect that such transfer or sale
may be effected without the registration of such Investor Common Stock under the
Securities Act, the

                                       5
<PAGE>

Company shall thereupon permit or cause its transfer agent (if any) to permit
such transfer or sale to be effected; provided, however, that if in such written
notice the transferring Investor represents and warrants to the Company that the
transfer or sale is to a purchaser or transferee whom the transferring
Shareholder knows or reasonably believes to be a "qualified institutional
buyer," as that term is defined in Rule 144A promulgated by the Securities and
Exchange Commission under the Act ("Rule 144A"), no opinion shall be required.

     4.4   Termination of Restrictions.
           ---------------------------

     (a)   Notwithstanding the foregoing provisions of this Article IV, the
restrictions imposed by this Article IV upon the transferability of Investor
Common Stock shall terminate as to any particular share of Investor Common Stock
when (1) such Investor Common Stock shall have been effectively registered under
the Act and sold by the Investor thereof in accordance with such registration,
or (2) a written opinion to the effect that such restrictions are no longer
required or necessary under any federal or state securities law or regulation
have been received from counsel for the Investor thereof (provided that such
counsel, and the form and substance of such opinion, are reasonably satisfactory
to the Company) or counsel for the Company, or (3) such Investor Common Stock
shall have been sold without registration under the Act in compliance with Rule
144, or (4) the Company is reasonably satisfied that the Investor shall, in
accordance with the terms of Subsection (k) of Rule 144, be entitled to sell
such Investor Common Stock pursuant to such Subsection, or (5) a letter or an
order shall have been issued to the Investor thereof by the staff of the
Securities and Exchange Commission or such Commission stating that no
enforcement action shall be recommended by such staff or taken by such
Commission, as the case may be, if such Investor Common Stock is transferred
without registration under the Securities Act in accordance with the conditions
set forth in such letter or order and such letter or order specifies that no
subsequent restrictions on transfer are required.

     (b)   Whenever the restrictions imposed by this Article IV shall terminate,
as hereinabove provided, the Investor of any particular share of Investor Common
Stock then outstanding as to which such restrictions shall have terminated shall
be entitled to receive from the Company, without expense to such Investor, one
or more new certificates for such Investor Common Stock not bearing the
restrictive legend set forth in Section 4.1 hereof.

     4.5   Compliance with Rule 144 and Rule 144A. At the written request of any
           --------------------------------------
Investor who proposes to sell any of such Common Stock in compliance with Rule
144, the Company shall furnish to such Investor, within ten (10) days after
receipt of request, a written statement as to whether or not the Company is in
compliance with the filing requirements of the Securities and Exchange
Commission as set forth in such Rule. For purposes of effecting compliance with
Rule 144A, in connection with any resales of any shares of Common Stock that
hereafter may be effected pursuant to the provisions of Rule 144A, any Investor
desiring to effect such resale and each prospective institutional purchaser of
such shares designated by such Investor shall have the right, at any time the
Company is not subject to Section 13 or 15(d) of the Securities and Exchange
Act, as amended, to obtain from the Company, upon the written request of such
holder and at the Company's expense the documents specified in Section (d)(4)(i)
of Rule 144A, as such rule may be amended from time to time.

                                       6
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     4.6   Non-Applicability of Restrictions on Transfer. Notwithstanding the
           ---------------------------------------------
provisions of Section 4.3 hereof, any record owner of Investor Common Stock may
from time to time transfer or recertificate all or a part of such record owner's
Investor Common Stock (i) to a nominee identified in writing to the Company as
being the nominee of or for such record owner, and any nominee of or for a
beneficial owner of Investor Common Stock identified in writing to the Company
as being the nominee of or for such beneficial owner may from time to time
transfer all or a part of the Investor Common Stock registered in the name of
such nominee but held as nominee on behalf of such beneficial owner, to such
beneficial owner, (ii) to an Affiliate of such record owner, or (iii) if such
record owner is a partnership or the nominee of a partnership, to a partner,
retired partner, or estate of a partner or retired partner, of such partnership,
so long as such transfer is in accordance with the transferee's interest in such
partnership and is without consideration; provided, however, that each such
transferee shall remain subject to all restrictions on the transfer of Investor
Common Stock herein contained.

                                   ARTICLE V
                                 MISCELLANEOUS

     5.1   Amendments; Waiver. This Agreement may be amended only in a writing
which is executed by the Company, and all of the Shareholders.

     5.2   Notices. Any and all notices or other communications required or
           -------
permitted to be delivered hereunder shall be deemed properly delivered if (a)
delivered personally, (b) mailed by first class, registered or certified mail,
return receipt requested, postage prepaid, (c) sent by next-day or overnight
mail or delivery or (d) sent by telecopy or telegram, to the parties listed on
Annex 1, or to such other address or to the attention of such other Person as
the recipient party has specified by prior written notice to the sending party.

     5.3   General.
           -------

     (a)   Binding Effect. It is expressly agreed and understood that this
Agreement is not to be deemed strictly personal to the parties hereunder, but
this Agreement shall also inure to the benefit of and be binding not only upon
the said parties hereto but also upon their respective heirs, executors,
administrators, personal and legal representatives, successors and assigns, and
all parties hereto agree for themselves and for their said heirs, executors,
administrators, personal and legal representatives, successors and assigns to be
bound by all of the provisions hereof and to execute at any time any documents
or instruments which may be necessary or proper to carry out the purpose and
intent of this Agreement. Notwithstanding the foregoing, the rights of the
Investors set forth herein shall inure only to the benefit of the Investors and
their "Permitted Transferees" (as such term is defined in the Registration
Agreement).

     (b)   Governing Law. The internal law of the State of Illinois will govern
all questions concerning the construction, validity and interpretation of this
Agreement, notwithstanding the fact that one or more of the parties now is or
may become a resident of or domiciled in a different state.

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     (c)   Superseding Agreement. This Agreement and all Exhibits hereto shall
supersede, revoke and nullify any and all agreements bearing prior date by or
between the Company and the Shareholders, or any of them, relating to or
restricting the transfer or disposition, whether voluntary or involuntary and
whether during their lives or at death, of any or all of the Shares. All such
agreements, and all promises, rights, duties and obligations established
pursuant thereto, are hereby rendered null and void. To the extent any notation
concerning this Agreement is deemed required in the By-Laws or Articles of
Incorporation of the Company, such notation shall be effected as promptly as
practicable hereafter.

     (d)   Counterparts and Gender References. This Agreement may be executed in
several counterparts (including by means of separate signature pages, which may
be attached hereto) by one or more of the parties, each of which shall be deemed
an original, and all of said counterparts (and signature pages) shall be deemed
to constitute or be part of one and the same instrument. One or more
counterparts of this Agreement may be delivered by facsimile, with the intention
that delivery by such means shall have the same effect as delivery of an
original counterpart thereof. All gender references shall be deemed modified to
fit the context.

     (e)   Severability. Should any particular provision of this Agreement be
adjudicated to be invalid or unenforceable such provision shall be deemed
deleted and the remainder of the Agreement, nevertheless, remain unaffected and
fully enforceable; further, to the extent any provision herewith is deemed
unenforceable by virtue of its scope but may be made enforceable by limitation
thereof, the parties hereto agree the same shall, nevertheless, be enforceable
to the fullest extent permissible under the laws and public policies applied in
the jurisdiction in which enforcement or interpretation is sought.

     (f)   Further Assurances. Upon request of the Company or any party hereto,
all parties hereto agree to promptly execute and deliver all such other
instruments and take all such other actions or any party hereto may reasonably
request from time to time in order to effectuate and carry out the purposes,
privileges, restrictions, rights and duties of the parties and other provisions
of this Agreement.

     (g)   No Waiver, Remedies Cumulative. No delay on the part of any party in
exercising any right, power or privilege under this Agreement shall operate as a
waiver thereof, nor shall any single or partial exercise of any right, power or
privilege hereunder preclude other or further exercise thereof, or the exercise
of any other right, power or privilege. Without limiting the generality of the
foregoing, nothing in this Agreement shall be deemed to preclude or be in lieu
of any right or remedy that any party may have at law or in equity or by statute
or otherwise against the Company or any other person based upon any fraud
(whether or not the matter to which the fraud related also constitutes a default
hereunder).

     (h)   Headings; Exhibits. The headings or other subdivisions in this
Agreement are intended solely for convenience or reference and shall be given no
effect in the construction or interpretation of this Agreement. All Exhibits
attached hereto are deemed incorporated herein by reference.

                                       8
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     (i)   Specific Performance. The parties hereby declare that it is
impossible to measure in money the damages which will accrue to a party hereto
by reason of a failure to perform any of the obligations under this Agreement
and that a breach hereof shall cause irreparable injury and, in addition to any
other right or remedy available to the parties hereto at law or in equity, any
injured party hereunder shall be entitled to enforcement by court injunction or
specific performance of the obligations of the Shareholders hereunder, without
the necessity for posting a bond. Notwithstanding the foregoing sentence,
nothing herein shall be construed as prohibiting any injured party hereunder
from also pursuing any other rights or remedies for such breach or threatened
breach, including receiving damages and attorneys' fees. The election of any
remedy shall not be construed as a waiver on the part of any injured party
hereunder of any rights such party might otherwise have at law or in equity,
which rights and remedies shall be cumulative.

     5.4   Termination. This Agreement shall terminate and be of no further
           -----------
force and effect upon the thirtieth (30th) day after a registration statement
with respect to the resale of all of the Investor Common Stock, upon such terms
and provisions as set forth in the Registration Agreement, becomes effective.

                                       9
<PAGE>

                     Shareholders' Agreement Signature Page

IN WITNESS WHEREOF, the Company and each of the Shareholders have signed this
Agreement, all on the day and year first above written.

DESIGN AUTOMATION SYSTEMS, INC.,         LJH PARTNERS LP, a Delaware limited
a Texas corporation d/b/a EpicEdge       partnership

                                         By:  Lamont Partners, LLC
By:  /s/ Charles H. Leaver, Jr.          Its: General Partner
   ---------------------------------
Its: President
                                         By:   /s/ Douglas S. Luke
                                            ---------------------------
                                         Its: Managing Member

EDGEWATER PRIVATE EQUITY FUND            WAIN INVESTMENT, LLC, an Ohio
III, L.P.                                limited liability company

By:  Edgewater III Management, L.P.      By:   /s/ Norman Wain
                                            ---------------------------
Its: General Partner                     Its:  Managing Partner

By:  Gordon Management, Inc.
Its: General Partner                           /s/ Gerald C. Allen
                                         ------------------------------
                                               Gerald C. Allen
By:   /s/ James Gordon
   ---------------------------------
Its:  President

ASPEN FINANCE INVESTORS I, LLC, a              /s/ John Paul DiJoria
                                         ------------------------------
Colorado limited liability company             John Paul DiJoria


By:  /s/ Howard S. Cohen                       /s/ Carl Rose
   ---------------------------------     ------------------------------
Its: Manager                                   Carl Rose

FLECK T.I.M.E. FUND, LP, a Connecticut
limited partnership                            /s/ Charles Leaver
                                         ------------------------------
                                               Charles Leaver
By:  /s/ Kathryn Fleck
   ---------------------------------
Its: Managing Partner
                                               /s/ Jeff Sexton
                                         ------------------------------
FLECK FAMILY PARTNERSHIP II, LP, a             Jeff Sexton
Florida limited partnership


                                       10
<PAGE>

By:  /s/ Barry Fleck                           /s/ Kelly Knake
   -------------------                   ------------------------------
Its: Managing Partner                          Kelly Knake

                                       11