Document:

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                                                                     EXHIBIT 4.4
                                                                     -----------

                                MATRIXONE, INC.

                                1999 Stock Plan
                                ---------------

1.   Purpose and Eligibility
     -----------------------

     The purpose of this 1999 Stock Plan (the "Plan") of MatrixOne, Inc. (the
                                               ----
"Company") is to provide stock options and other equity interests in the Company
--------
(each an "Award") to employees, officers, directors, consultants and advisors of
          -----
the Company and its Subsidiaries, all of whom are eligible to receive Awards
under the Plan. Any person to whom an Award has been granted under the Plan is
called a "Participant". Additional definitions are contained in Section 8.
          -----------

2.   Administration
     --------------

     a.   Administration by Board of Directors.  The Plan will be administered
          ------------------------------------
by the Board of Directors of the Company (the "Board"). The Board, in its sole
                                               -----
discretion, shall have the authority to grant and amend Awards, to adopt, amend
and repeal rules relating to the Plan and to interpret and correct the
provisions of the Plan and any Award. All decisions by the Board shall be final
and binding on all interested persons. Neither the Company nor any member of the
Board shall be liable for any action or determination relating to the Plan.

     b.   Appointment of Committees.  To the extent permitted by applicable law,
          -------------------------
the Board may delegate any or all of its powers under the Plan to one or more
committees or subcommittees of the Board (a "Committee"). All references in the
                                             ---------
Plan to the "Board" shall mean such Committee or the Board.
             -----

     c.   Delegation to Executive Officers. To the extent permitted by
          --------------------------------
applicable law, the Board may delegate to one or more executive officers of the
Company the power to grant Awards and exercise such other powers under the Plan
as the Board may determine, provided that the Board shall fix the maximum number
of Awards to be granted and the maximum number of shares issuable to any one
Participant pursuant to Awards granted by such executive officers and shall
establish such other terms and conditions to the power of the executive officers
as the Board so chooses.

3.   Stock Available for Awards
     --------------------------

     a.   Number of Shares.  Subject to adjustment under Section 3(c), the
          ----------------
aggregate number of shares of Common Stock of the Company (the "Common Stock")
                                                                ------------
that may be issued pursuant to the Plan is 1,500,000 shares. If any Award
expires, or is terminated, surrendered or forfeited, in whole or in part, the
unissued Common Stock covered by such Award shall again be available for the
grant of Awards under the Plan. If shares of Common Stock issued pursuant to the
Plan are repurchased by, or are surrendered or forfeited to, the Company at no
more than cost,
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such shares of Common Stock shall again be available for the grant of Awards
under the Plan; provided, however, that the cumulative number of such shares
that may be so reissued under the Plan will not exceed 1,500,000 shares. Shares
issued under the Plan may consist in whole or in part of authorized but unissued
shares or treasury shares.

     b.   Per-Participant Limit.  Subject to adjustment under Section 3(c), no
          ---------------------
Participant may be granted Awards during any one fiscal year to purchase more
than 300,000 shares of Common Stock.

     c.   Adjustment to Common Stock.  In the event of any stock split, stock
          --------------------------
dividend, extraordinary cash dividend, recapitalization, reorganization, merger,
consolidation, combination, exchange of shares, liquidation, spin-off, split-up,
or other similar change in capitalization or event, (i) the number and class of
securities available for Awards under the Plan and the per-Participant share
limit, (ii) the number and class of securities, vesting schedule and exercise
price per share subject to each outstanding Option, (iii) the repurchase price
per security subject to repurchase, and (iv) the terms of each other outstanding
stock-based Award shall be adjusted by the Company (or substituted Awards may be
made) to the extent the Board shall determine, in good faith, that such an
adjustment (or substitution) is appropriate. If Section 7(e)(i) applies for any
event, this Section 3(c) shall not be applicable.

4.   Stock Options
     -------------

     a.   General.  The Board may grant options to purchase Common Stock (each,
          -------
an "Option") and determine the number of shares of Common Stock to be covered by
    ------
each Option, the exercise price of each Option and the conditions and
limitations applicable to the exercise of each Option and the Common Stock
issued upon the exercise of each Option, including vesting provisions,
repurchase provisions and restrictions relating to applicable federal or state
securities laws, as it considers advisable.

     b.   Incentive Stock Options.  An Option that the Board intends to be an
          -----------------------
"incentive stock option" as defined in Section 422 of the Code (an "Incentive
                                                                    ---------
Stock Option") shall be granted only to employees of the Company and shall be
------------
subject to and shall be construed consistently with the requirements of Section
422 of the Code. The Board and the Company shall have no liability if an Option
or any part thereof that is intended to be an Incentive Stock Option does not
qualify as such. An Option or any part thereof that does not qualify as an
Incentive Stock Option, or an Option that could qualify but is intentionally not
granted as an Incentive Stock Option, is referred to herein as a "Nonstatutory
                                                                  ------------
Stock Option".
------------

     c.   Exercise Price.  The Board shall establish the exercise price (or
          --------------
determine the method by which the exercise price shall be determined) at the
time each Option is granted and specify it in the applicable option agreement.

     d.   Duration of Options.  Each Option shall be exercisable at such times
          -------------------
and be subject to such terms and conditions as the Board may specify in the
applicable option agreement.

                                      -2-
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     e.   Exercise of Option.  Options may be exercised only by delivery to the
          ------------------
Company of a written notice of exercise signed by the proper person together
with payment in full as specified in Section 4(f) for the number of shares for
which the Option is exercised.

     f.   Payment Upon Exercise.  Common Stock purchased upon the exercise of an
          ---------------------
Option shall be paid for by one or any combination of the following forms of
payment:

          (i)   by check payable to the order of the Company;

          (ii)  except as otherwise explicitly provided in the applicable option
agreement, and only if the Common Stock is then publicly traded, delivery of an
irrevocable and unconditional undertaking by a creditworthy broker to deliver
promptly to the Company sufficient funds to pay the exercise price, or delivery
by the Participant to the Company of a copy of irrevocable and unconditional
instructions to a creditworthy broker to deliver promptly to the Company cash or
a check sufficient to pay the exercise price; or

          (iii) to the extent explicitly provided in the applicable option
agreement, by (x) delivery of shares of Common Stock owned by the Participant
valued at fair market value (as determined by the Board or as determined
pursuant to the applicable option agreement), or (y) payment of such other
lawful consideration as the Board may determine.

5.   Restricted Stock
     ----------------

     a.   Grants.  The Board may grant Awards entitling recipients to acquire
          ------
shares of Common Stock, subject to (i) delivery to the Company by the
Participant of a check in an amount at least equal to the par value of the
shares purchased, and (ii) the right of the Company to repurchase all or part of
such shares at their issue price or other stated or formula price from the
Participant in the event that conditions specified by the Board in the
applicable Award are not satisfied prior to the end of the applicable
restriction period or periods established by the Board for such Award (each, a
"Restricted Stock Award").
-----------------------

     b.   Terms and Conditions. The Board shall determine the terms and
          --------------------
conditions of any such Restricted Stock Award. Any stock certificates issued in
respect of a Restricted Stock Award shall be registered in the name of the
Participant and, unless otherwise determined by the Board, deposited by the
Participant, together with a stock power endorsed in blank, with the Company (or
its designee). After the expiration of the applicable restriction periods, the
Company (or such designee) shall deliver the certificates no longer subject to
such restrictions to the Participant or, if the Participant has died, to the
beneficiary designated by a Participant, in a manner determined by the Board, to
receive amounts due or exercise rights of the Participant in the event of the
Participant's death (the "Designated Beneficiary"). In the absence of an
                          ----------------------
effective designation by a Participant, Designated Beneficiary shall mean the
Participant's estate.

                                      -3-
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6.   Other Stock-Based Awards
     ------------------------

     The Board shall have the right to grant other Awards based upon the Common
Stock having such terms and conditions as the Board may determine, including,
without limitation, the grant of shares based upon certain conditions, the grant
of securities convertible into Common Stock and the grant of stock appreciation
rights, phantom stock awards or stock units.

7.   General Provisions Applicable to Awards
     ---------------------------------------

     a.   Transferability of Awards. Except as the Board may otherwise determine
          -------------------------
or provide in an Award, Awards shall not be sold, assigned, transferred, pledged
or otherwise encumbered by the person to whom they are granted, either
voluntarily or by operation of law, except by will or the laws of descent and
distribution, and, during the life of the Participant, shall be exercisable only
by the Participant. References to a Participant, to the extent relevant in the
context, shall include references to authorized transferees. Notwithstanding the
foregoing, Nonstatutory Stock Options shall also be assignable or transferable
pursuant to: (i) a valid domestic relations order or (ii) to: (A) parents of the
grantee, (B) issue of the parents of the grantee, (C) parents of the grantee's
spouse, (D) issue of the parents of the grantee's spouse, (E) spouses of any
such issue, (F) the legal guardian of any such issue and/or spouses, (G) one or
more trusts for the primary benefit of any such issue, spouses and/or charitable
organizations described in provision (I) below, which trusts are either
irrevocable or restricted by their terms such that they may not be amended to
provide distribution of any Stock Right to anyone other than such issue,
spouses, and/or charitable organizations, (H) the custodian for any such issue
under the Uniform Transfers to Minors Act or corresponding statute of any
jurisdiction, or (I) a charitable organization described in Section 170(c) of
the Internal Revenue Code, or any successor thereto (the "Code") including but
not limited to private foundations and supporting organizations which have been
established by the grantee during the grantee's lifetime, and which have
obtained tax exempt status under Section 501(c)(3) of the Code; and in each such
case only to the extent that such transfer is authorized by either the Chief
Executive Officer or the Chief Financial Officer of the Company; and thereafter
the transferee shall have all such rights of the grantee, provided, however,
that any provisions relating to employment or business relationship of the
grantee (such as option termination provisions) shall be deemed to survive such
transfer and the grantee's actual period of employment or business relationship
shall be the relevant measurement period for purposes thereof.

     b.   Documentation.  Each Award under the Plan shall be evidenced by a
          -------------
written instrument in such form as the Board shall determine or as executed by
an officer of the Company pursuant to authority delegated by the Board. Each
Award may contain terms and conditions in addition to those set forth in the
Plan provided that such terms and conditions do not contravene the provisions of
the Plan.

     c.   Board Discretion. The terms of each type of Award need not be
          ----------------
identical, and the Board need not treat Participants uniformly.

                                      -4-
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     d.   Termination of Status.  The Board shall determine the effect on an
          ---------------------
Award of the disability, death, retirement, authorized leave of absence or other
change in the employment or other status of a Participant and the extent to
which, and the period during which, the Participant, or the Participant's legal
representative, conservator, guardian or Designated Beneficiary, may exercise
rights under the Award.

     e.   Acquisition of the Company
          --------------------------

          (i)  Consequences of an Acquisition.
               ------------------------------

               (A)  Acquisition Intended to be Accounted for as a Pooling-of-
                    ---------------------------------------------------------
Interests.  Upon the consummation of an Acquisition intended to be accounted for
---------
as a pooling of interests: (x) all outstanding Awards shall remain the
obligation of the Company or be assumed by the surviving or acquiring entity,
and there shall be automatically substituted for the shares of Common Stock then
subject to such Awards the consideration payable with respect to the outstanding
shares of Common Stock in connection with the Acquisition and (y) the vesting
provisions of all then unvested Awards shall become accelerated by a period of
24 months.

               (B)  Acquisition Intended to be Accounted for under the Purchase
                    -----------------------------------------------------------
Method. Unless otherwise expressly provided in the applicable Option or Award,
------
upon the occurrence of an Acquisition intended to be accounted for under the
purchase method, (x) the vesting provisions of all then unvested Awards shall
become accelerated by a period of 24 months and (y) the Board or the board of
directors of the surviving or acquiring entity (as used in this Section
7(e)(i)(B), also the "Board"), shall, as to outstanding Awards (on the same
                      -----
basis or on different bases, as the Board shall specify), make appropriate
provision for the continuation of such Awards by the Company or the assumption
of such Awards by the surviving or acquiring entity and by substituting on an
equitable basis for the shares then subject to such Awards either (i) the
consideration payable with respect to the outstanding shares of Common Stock in
connection with the Acquisition, (ii) shares of stock of the surviving or
acquiring corporation or (iii) such other securities as the Board deems
appropriate, the fair market value of which (as determined by the Board in its
sole discretion) shall not materially differ from the fair market value of the
shares of Common Stock subject to such Awards immediately preceding the
Acquisition. In addition to or in lieu of the foregoing, with respect to
outstanding Options, the Board may, upon written notice to the affected
optionees, provide (a) that one or more Options then outstanding shall become
immediately exercisable in full; (b) that such Options must be exercised within
a specified number of days of the date of such notice, at the end of which
period such Options shall terminate; or (c) that one or more Options then
outstanding shall be terminated in exchange for a cash payment equal to the
excess of the fair market value (as determined by the Board in its sole
discretion) for the shares subject to such Options over the exercise price
thereof.

               (C)  Acquisition Defined.  An "Acquisition" shall mean: (x) the
                    -------------------       -----------
sale of the Company by merger in which the shareholders of the Company in their
capacity as such no longer own a majority of the outstanding equity securities
of the Company (or its successor); or (y) any sale of all or substantially all
of the assets or capital stock of the Company (other than in a

                                      -5-
<PAGE>

spin-off or similar transaction) or (z) any other acquisition of the business of
the Company, as determined by the Board.

          (ii)   Assumption of Options Upon Certain Events.  In connection with
                 -----------------------------------------
a merger or consolidation of an entity with the Company or the acquisition by
the Company of property or stock of an entity, the Board may grant Awards under
the Plan in substitution for stock and stock-based awards issued by such entity
or an affiliate thereof. The substitute Awards shall be granted on such terms
and conditions as the Board considers appropriate in the circumstances.

          (iii)  Pooling-of Interests-Accounting.  If the Company proposes to
                 -------------------------------
engage in an Acquisition intended to be accounted for as a pooling-of-interests,
and in the event that the provisions of this Plan or of any Award hereunder, or
any actions of the Board taken in connection with such Acquisition, are
determined by the Company's or the acquiring company's independent public
accountants to cause such Acquisition to fail to be accounted for as a pooling-
of-interests, then such provisions or actions shall be amended or rescinded by
the Board, without the consent of any Participant, to be consistent with
pooling-of-interests accounting treatment for such Acquisition.

          (iv)   Parachute Awards. Notwithstanding the provisions of Section
                 ----------------
7(e)(i)(A), if, in connection with an Acquisition described therein, a tax under
Section 4999 of the Code would be imposed on the Participant (after taking into
account the exceptions set forth in Sections 280G(b)(4) and 280G(b)(5) of the
Code), then the number of Awards which shall become exercisable, realizable or
vested as provided in such section shall be reduced (or delayed), to the minimum
extent necessary, so that no such tax would be imposed on the Participant (the
Awards not becoming so accelerated, realizable or vested, the "Parachute
                                                               ---------
Awards"); provided, however, that if the "aggregate present value" of the
                                          -----------------------
Parachute Awards would exceed the tax that, but for this sentence, would be
imposed on the Participant under Section 4999 of the Code in connection with the
Acquisition, then the Awards shall become immediately exercisable, realizable
and vested without regard to the provisions of this sentence. For purposes of
the preceding sentence, the "aggregate present value" of an Award shall be
                             -----------------------
calculated on an after-tax basis (other than taxes imposed by Section 4999 of
the Code) and shall be based on economic principles rather than the principles
set forth under Section 280G of the Code and the regulations promulgated
thereunder. All determinations required to be made under this Section 7(e)(iv)
shall be made by the Company.

     f.   Withholding.  Each Participant shall pay to the Company, or make
          -----------
provisions satisfactory to the Company for payment of, any taxes required by law
to be withheld in connection with Awards to such Participant no later than the
date of the event creating the tax liability. The Board may allow Participants
to satisfy such tax obligations in whole or in part by transferring shares of
Common Stock, including shares retained from the Award creating the tax
obligation, valued at their fair market value (as determined by the Board or as
determined pursuant to the applicable option agreement). The Company may, to the
extent permitted by law, deduct any such tax obligations from any payment of any
kind otherwise due to a Participant.

                                      -6-
<PAGE>

     g.   Amendment of Awards.  The Board may amend, modify or terminate any
          -------------------
outstanding Award including, but not limited to, substituting therefor another
Award of the same or a different type, changing the date of exercise or
realization, and converting an Incentive Stock Option to a Nonstatutory Stock
Option, provided that, except as otherwise provided in Section 7(e)(iii), the
Participant's consent to such action shall be required unless the Board
determines that the action, taking into account any related action, would not
materially and adversely affect the Participant.

     h.   Conditions on Delivery of Stock.  The Company will not be obligated to
          -------------------------------
deliver any shares of Common Stock pursuant to the Plan or to remove
restrictions from shares previously delivered under the Plan until (i) all
conditions of the Award have been met or removed to the satisfaction of the
Company, (ii) in the opinion of the Company's counsel, all other legal matters
in connection with the issuance and delivery of such shares have been satisfied,
including any applicable securities laws and any applicable stock exchange or
stock market rules and regulations, and (iii) the Participant has executed and
delivered to the Company such representations or agreements as the Company may
consider appropriate to satisfy the requirements of any applicable laws, rules
or regulations.

     i.   Acceleration. The Board may at any time provide that any Options shall
          ------------
become immediately exercisable in full or in part, that any Restricted Stock
Awards shall be free of some or all restrictions, or that any other stock-based
Awards may become exercisable in full or in part or free of some or all
restrictions or conditions, or otherwise realizable in full or in part, as the
case may be, despite the fact that the foregoing actions may (i) cause the
application of Sections 280G and 4999 of the Code if a change in control of the
Company occurs, or (ii) disqualify all or part of the Option as an Incentive
Stock Option.

8.   Miscellaneous
     -------------

     a.  Definitions.
         -----------

               (i)   "Company," for purposes of eligibility under the Plan,
                      --------
shall include any present or future subsidiary corporations of MatrixOne, Inc.,
as defined in Section 424(f) of the Code (a "Subsidiary"), and any present or
                                             ----------
future parent corporation of MatrixOne, Inc., as defined in Section 424(e) of
the Code. For purposes of Awards other than Incentive Stock Options, the term
"Company" shall include any other business venture in which the Company has a
--------
direct or indirect significant interest, as determined by the Board in its sole
discretion.

               (ii)  "Code" means the Internal Revenue Code of 1986, as amended,
                      ----
and any regulations promulgated thereunder.

               (iii) "employee" for purposes of eligibility under the Plan (but
                      --------
not for purposes of Section 4(b)) shall include a person to whom an offer of
employment has been extended by the Company.

                                      -7-
<PAGE>

     b.   No Right To Employment or Other Status.  No person shall have any
          --------------------------------------
claim or right to be granted an Award, and the grant of an Award shall not be
construed as giving a Participant the right to continued employment or any other
relationship with the Company. The Company expressly reserves the right at any
time to dismiss or otherwise terminate its relationship with a Participant free
from any liability or claim under the Plan.

     c.   No Rights As Stockholder.  Subject to the provisions of the applicable
          ------------------------
Award, no Participant or Designated Beneficiary shall have any rights as a
stockholder with respect to any shares of Common Stock to be distributed with
respect to an Award until becoming the record holder thereof.

     d.   Effective Date and Term of Plan.  The Plan shall become effective on
          -------------------------------
the date on which it is adopted by the Board. No Awards shall be granted under
the Plan after the completion of ten years from the date on which the Plan was
adopted by the Board, but Awards previously granted may extend beyond that date.

     e.   Amendment of Plan.  The Board may amend, suspend or terminate the Plan
          -----------------
or any portion thereof at any time, subject, in the case of amendments, to any
applicable statutory or regulatory requirements to obtain shareholder approval
when and if so required.

     f.   Governing Law. The provisions of the Plan and all Awards made
          -------------
hereunder shall be governed by and interpreted in accordance with the laws of
Delaware, without regard to any applicable conflicts of law.

                                    Adopted by the Board of Directors on
                                    January 20, 2000

                                    Approved by the stockholders on
                                    January 20, 2000

                                      -8-<PAGE>

                                                                     EXHIBIT 4.7
                                                                     -----------

                                MATRIXONE, INC.

                       2000 EMPLOYEE STOCK PURCHASE PLAN

Article 1 - Purpose.
-------------------

     This 2000 Employee Stock Purchase Plan (the "Plan") is intended to
encourage stock ownership by all eligible employees of MatrixOne, Inc. (the
"Company"), a Delaware corporation, and its participating subsidiaries (as
defined in Article 17) so that they may share in the growth of the Company by
acquiring or increasing their proprietary interest in the Company. The Plan is
designed to encourage eligible employees to remain in the employ of the Company
and its participating subsidiaries. The Plan is intended to constitute an
"employee stock purchase plan" within the meaning of Section 423(b) of the
Internal Revenue Code of 1986, as amended (the "Code").

Article 2 - Administration of the Plan.
--------------------------------------

     The Plan may be administered by a committee appointed by the Board of
Directors of the Company (the "Committee"). The Committee shall consist of not
less than two members of the Company's Board of Directors. The Board of
Directors may from time to time remove members from, or add members to, the
Committee. Vacancies on the Committee, howsoever caused, shall be filled by the
Board of Directors. The Committee may select one of its members as Chairman, and
shall hold meetings at such times and places as it may determine. Acts by a
majority of the Committee, or acts reduced to or approved in writing by a
majority of the members of the Committee, shall be the valid acts of the
Committee.

     The interpretation and construction by the Committee of any provisions of
the Plan or of any option granted under it shall be final, unless otherwise
determined by the Board of Directors. The Committee may from time to time adopt
such rules and regulations for carrying out the Plan as it may deem best,
provided that any such rules and regulations shall be applied on a uniform basis
to all employees under the Plan. No member of the Board of Directors or the
Committee shall be liable for any action or determination made in good faith
with respect to the Plan or any option granted under it.

     In the event the Board of Directors fails to appoint or refrains from
appointing a Committee, the Board of Directors shall have all power and
authority to administer the Plan. In such event, the word "Committee" wherever
used herein shall be deemed to mean the Board of Directors.

Article 3 - Eligible Employees.
------------------------------

     All employees of the Company or any of its participating subsidiaries whose
customary employment is more than 20 hours per week and for more than five
months in any calendar
<PAGE>

                                      -2-

year shall be eligible to receive options under the Plan to purchase common
stock of the Company, and all eligible employees shall have the same rights and
privileges hereunder. Persons who are eligible employees on the first business
day of any Payment Period (as defined in Article 5) shall receive their options
as of such day. Persons who become eligible employees after any date on which
options are granted under the Plan shall be granted options on the first day of
the next succeeding Payment Period on which options are granted to eligible
employees under the Plan. In no event, however, may an employee be granted an
option if such employee, immediately after the option was granted, would be
treated as owning stock possessing five percent or more of the total combined
voting power or value of all classes of stock of the Company or of any parent
corporation or subsidiary corporation, as the terms "parent corporation" and
"subsidiary corporation" are defined in Section 424(e) and (f) of the Code. For
purposes of determining stock ownership under this paragraph, the rules of
Section 424(d) of the Code shall apply, and stock which the employee may
purchase under outstanding options shall be treated as stock owned by the
employee.

Article 4 - Stock Subject to the Plan.
-------------------------------------

     The stock subject to the options under the Plan shall be shares of the
Company's authorized but unissued common stock, par value $.01 per share (the
"Common Stock"), or shares of Common Stock reacquired by the Company, including
shares purchased in the open market. The aggregate number of shares which may be
issued pursuant to the Plan is 1,350,000, subject to adjustment as provided in
Article 12. If any option granted under the Plan shall expire or terminate for
any reason without having been exercised in full or shall cease for any reason
to be exercisable in whole or in part, the unpurchased shares subject thereto
shall again be available under the Plan.

Article 5 - Payment Period and Stock Options.
--------------------------------------------

     The first Payment Period during which payroll deductions will be
accumulated under the Plan shall commence on the later to occur of May 1, 2000
and the first day of the first calendar month following effectiveness of the
Form S-8 registration statement filed with the Securities and Exchange
Commission covering the shares to be issued pursuant to the Plan and shall end
on October 31, 2000. For the remainder of the duration of the Plan, Payment
Periods shall consist of the six-month periods commencing on November 1 and May
1 and ending on April 30 and October 31 of each calendar year.

     Twice each year, on the first business day of each Payment Period, the
Company will grant to each eligible employee who is then a participant in the
Plan an option to purchase on the last day of such Payment Period, at the Option
Price hereinafter provided for, a maximum of 2,250 shares, on condition that
such employee remains eligible to participate in the Plan throughout the
remainder of such Payment Period and subject to the limitation set forth in
Article 4. The participant shall be entitled to exercise the option so granted
only to the extent of the participant's accumulated payroll deductions on the
last day of such Payment Period. If the participant's accumulated payroll
deductions on the last day of the Payment Period would
<PAGE>

                                      -3-

enable the participant to purchase more than 2,250 shares except for the 2,250-
share limitation, the excess of the amount of the accumulated payroll deductions
over the aggregate purchase price of the 2,250 shares shall be promptly refunded
to the participant by the Company, without interest. The Option Price per share
for each Payment Period shall be the lesser of (i) 85% of the average market
price of the Common Stock on the first business day of the Payment Period and
(ii) 85% of the average market price of the Common Stock on the last business
day of the Payment Period, in either event rounded up to the nearest cent. The
foregoing limitations on the number of shares subject to option and the Option
Price shall be subject to adjustment as provided in Article 12.

     For purposes of the Plan, the term "average market price" on any date means
(i) the average (on that date) of the high and low prices of the Common Stock on
the principal national securities exchange on which the Common Stock is traded,
if the Common Stock is then traded on a national securities exchange; or (ii)
the last reported sale price (on that date) of the Common Stock on the Nasdaq
National Market, if the Common Stock is not then traded on a national securities
exchange; or (iii) the average of the closing bid and asked prices last quoted
(on that date) by an established quotation service for over-the-counter
securities, if the Common Stock is not reported on the Nasdaq National Market;
or (iv) if the Common Stock is not publicly traded, the fair market value of the
Common Stock as determined by the Committee after taking into consideration all
factors which it deems appropriate, including, without limitation, recent sale
and offer prices of the Common Stock in private transactions negotiated at arm's
length.

     For purposes of the Plan, the term "business day" means a day on which
there is trading on the Nasdaq National Market or the aforementioned national
securities exchange, whichever is applicable pursuant to the preceding
paragraph; and if neither is applicable, a day that is not a Saturday, Sunday or
legal holiday in the Commonwealth of Massachusetts.

     No employee shall be granted an option which permits the employee's right
to purchase stock under the Plan, and under all other Section 423(b) employee
stock purchase plans of the Company and any parent or subsidiary corporations,
to accrue at a rate which exceeds $25,000 of fair market value of such stock
(determined on the date or dates that options on such stock were granted) for
each calendar year in which such option is outstanding at any time. The purpose
of the limitation in the preceding sentence is to comply with Section 423(b)(8)
of the Code. If the participant's accumulated payroll deductions on the last day
of the Payment Period would otherwise enable the participant to purchase Common
Stock in excess of the Section 423(b)(8) limitation described in this paragraph,
the excess of the amount of the accumulated payroll deductions over the
aggregate purchase price of the shares actually purchased shall be promptly
refunded to the participant by the Company, without interest.

Article 6 - Exercise of Option.
------------------------------

     Each eligible employee who continues to be a participant in the Plan on the
last day of a Payment Period shall be deemed to have exercised his or her option
on such date and shall be deemed to have purchased from the Company such number
of full shares of Common Stock
<PAGE>

                                      -4-

reserved for the purpose of the Plan as the participant's accumulated payroll
deductions on such date will pay for at the Option Price, subject to the 2,250
share limit of the option, and the Section 423(b)(8) limitation described in
Article 5. If the individual is not a participant on the last day of a Payment
Period, then he or she shall not be entitled to exercise his or her option. Only
full shares of Common Stock may be purchased under the Plan. Unused payroll
deductions remaining in a participant's account at the end of a Payment Period
by reason of the inability to purchase a fractional share shall be carried
forward to the next Payment Period.

Article 7 - Authorization for Entering the Plan.
-----------------------------------------------

     An employee may elect to enter the Plan by filling out, signing and
delivering to the Company an authorization:

          A.  Stating the percentage to be deducted regularly from the
employee's pay;

          B.  Authorizing the purchase of stock for the employee in each Payment
Period in accordance with the terms of the Plan; and

          C.  Specifying the exact name or names in which stock purchased for
the employee is to be issued as provided under Article 11 hereof.

Such authorization must be received by the Company at least ten days before the
first day of the next succeeding Payment Period and shall take effect only if
the employee is an eligible employee on the first business day of such Payment
Period.

     Unless a participant files a new authorization or withdraws from the Plan,
the deductions and purchases under the authorization the participant has on file
under the Plan will continue from one Payment Period to succeeding Payment
Periods as long as the Plan remains in effect.

     The Company will accumulate and hold for each participant's account the
amounts deducted from his or her pay. No interest will be paid on these amounts.

Article 8 - Maximum Amount of Payroll Deductions.
------------------------------------------------

     An employee may authorize payroll deductions in an amount (expressed as a
whole percentage) not less than one percent (1%) but not more than ten percent
(10%) of the employee's total compensation, including base pay or salary and any
overtime, bonuses or commissions.

Article 9 - Change in Payroll Deductions.
----------------------------------------

     Deductions may not be increased or decreased during a Payment Period.
However, a participant may withdraw in full from the Plan.
<PAGE>

                                      -5-

Article 10 - Withdrawal from the Plan.
-------------------------------------

     A participant may withdraw from the Plan (in whole but not in part) at any
time prior to the last day of a Payment Period by delivering a withdrawal notice
to the Company.

     To re-enter the Plan, an employee who has previously withdrawn must file a
new authorization at least ten days before the first day of the next Payment
Period in which he or she wishes to participate. The employee's re-entry into
the Plan becomes effective at the beginning of such Payment Period, provided
that he or she is an eligible employee on the first business day of the Payment
Period.

Article 11 - Issuance of Stock.
------------------------------

     Certificates for stock issued to participants shall be delivered as soon as
practicable after each Payment Period by the Company's transfer agent.

     Stock purchased under the Plan shall be issued only in the name of the
participant, or if the participant's authorization so specifies, in the name of
the participant and another person of legal age as joint tenants with rights of
survivorship.

Article 12 - Adjustments.
------------------------

     Upon the happening of any of the following described events, a
participant's rights under options granted under the Plan shall be adjusted as
hereinafter provided:

          A.   In the event that the shares of Common Stock shall be subdivided
or combined into a greater or smaller number of shares or if, upon a
reorganization, split-up, liquidation, recapitalization or the like of the
Company, the shares of Common Stock shall be exchanged for other securities of
the Company, each participant shall be entitled, subject to the conditions
herein stated, to purchase such number of shares of Common Stock or amount of
other securities of the Company as were exchangeable for the number of shares of
Common Stock that such participant would have been entitled to purchase except
for such action, and appropriate adjustments shall be made in the purchase price
per share to reflect such subdivision, combination or exchange; and

          B.   In the event the Company shall issue any of its shares as a stock
dividend upon or with respect to the shares of stock of the class which shall at
the time be subject to option hereunder, each participant upon exercising such
an option shall be entitled to receive (for the purchase price paid upon such
exercise) the shares as to which the participant is exercising his or her option
and, in addition thereto (at no additional cost), such number of shares of the
class or classes in which such stock dividend or dividends were declared or
paid, and such amount of cash in lieu of fractional shares, as is equal to the
number of shares thereof and the amount of cash in lieu of fractional shares,
respectively, which the participant would have received if the participant had
been the holder of the shares as to which the participant is
<PAGE>

                                      -6-

exercising his or her option at all times between the date of the granting of
such option and the date of its exercise.

     Upon the happening of any of the foregoing events, the class and aggregate
number of shares set forth in Article 4 hereof which are subject to options
which have been or may be granted under the Plan and the limitation set forth in
the second paragraph of Article 5 shall also be appropriately adjusted to
reflect the events specified in paragraphs A and B above. Notwithstanding the
foregoing, any adjustments made pursuant to paragraphs A or B shall be made only
after the Committee, based on advice of counsel for the Company, determines
whether such adjustments would constitute a "modification" (as that term is
defined in Section 424 of the Code). If the Committee determines that such
adjustments would constitute a modification, it may refrain from making such
adjustments.

     If the Company is to be consolidated with or acquired by another entity in
a merger, a sale of all or substantially all of the Company's assets or
otherwise (an "Acquisition"), the Committee or the board of directors of any
entity assuming the obligations of the Company hereunder (the "Successor Board")
shall, with respect to options then outstanding under the Plan, either (i) make
appropriate provision for the continuation of such options by arranging for the
substitution on an equitable basis for the shares then subject to such options
either (a) the consideration payable with respect to the outstanding shares of
the Common Stock in connection with the Acquisition, (b) shares of stock of the
successor corporation, or a parent or subsidiary of such corporation, or (c)
such other securities as the Successor Board deems appropriate, the fair market
value of which shall not materially exceed the fair market value of the shares
of Common Stock subject to such options immediately preceding the Acquisition;
or (ii) terminate each participant's options in exchange for a cash payment
equal to the excess of (a) the fair market value on the date of the Acquisition,
of the number of shares of Common Stock that the participant's accumulated
payroll deductions as of the date of the Acquisition could purchase, at an
option price determined with reference only to the first business day of the
applicable Payment Period and subject to the 2,250-share, Code Section 423(b)(8)
and fractional-share limitations on the amount of stock a participant would be
entitled to purchase, over (b) the result of multiplying such number of shares
by such option price.

     The Committee or Successor Board shall determine the adjustments to be made
under this Article 12, and its determination shall be conclusive.

Article 13 - No Transfer or Assignment of Employee's Rights.
-----------------------------------------------------------

     An option granted under the Plan may not be transferred or assigned and may
be exercised only by the participant.

Article 14 - Termination of Employee's Rights.
---------------------------------------------

     Whenever a participant ceases to be an eligible employee because of
retirement, voluntary or involuntary termination, resignation, layoff,
discharge, death or for any other reason, his or her rights under the Plan shall
immediately terminate, and the Company shall
<PAGE>

                                      -7-

promptly refund, without interest, the entire balance of his or her payroll
deduction account under the Plan. Notwithstanding the foregoing, eligible
employment shall be treated as continuing intact while a participant is on
military leave, sick leave or other bona fide leave of absence, for up to 90
days, or for so long as the participant's right to re-employment is guaranteed
either by statute or by contract, if longer than 90 days.

     If a participant's payroll deductions are interrupted by any legal process,
a withdrawal notice will be considered as having been received from the
participant on the day the interruption occurs.

Article 15 - Termination and Amendments to Plan.
-----------------------------------------------

     Unless terminated sooner, as provided below, the Plan shall terminate on
December 9, 2009. The Plan may be terminated at any time by the Company's Board
of Directors but such termination shall not affect options then outstanding
under the Plan. It will terminate in any case when all or substantially all of
the unissued shares of stock reserved for the purposes of the Plan have been
purchased. If at any time shares of stock reserved for the purpose of the Plan
remain available for purchase but not in sufficient number to satisfy all then
unfilled purchase requirements, the available shares shall be apportioned among
participants in proportion to the amount of payroll deductions accumulated on
behalf of each participant that would otherwise be used to purchase stock, and
the Plan shall terminate. Upon such termination or any other termination of the
Plan, all payroll deductions not used to purchase stock will be refunded,
without interest.

     The Committee or the Board of Directors may from time to time adopt
amendments to the Plan provided that, without the approval of the stockholders
of the Company, no amendment may (i) increase the number of shares that may be
issued under the Plan; (ii) change the class of employees eligible to receive
options under the Plan, if such action would be treated as the adoption of a new
plan for purposes of Section 423(b) of the Code; or (iii) cause Rule 16b-3 under
the Securities Exchange Act of 1934 to become inapplicable to the Plan.

Article 16 - Limits on Sale of Stock Purchased under the Plan.
-------------------------------------------------------------

     The Plan is intended to provide shares of Common Stock for investment and
not for resale. The Company does not, however, intend to restrict or influence
any employee in the conduct of his or her own affairs. An employee may,
therefore, sell stock purchased under the Plan at any time the employee chooses,
subject to compliance with any applicable federal or state securities laws and
subject to any restrictions imposed under Article 21 to ensure that tax
withholding obligations are satisfied. THE EMPLOYEE ASSUMES THE RISK OF ANY
MARKET FLUCTUATIONS IN THE PRICE OF THE STOCK.
<PAGE>

                                      -8-

Article 17 - Participating Subsidiaries.
---------------------------------------

     The term "participating subsidiary" shall mean any present or future
subsidiary of the Company, as that term is defined in Section 424(f) of the
Code, which is designated from time to time by the Board of Directors to
participate in the Plan. The Board of Directors shall have the power to make
such designation before or after the Plan is approved by the stockholders.

Article 18 - Optionees Not Stockholders.
---------------------------------------

     Neither the granting of an option to an employee nor the deductions from
his or her pay shall constitute such employee a stockholder of the shares
covered by an option until such shares have been actually purchased by the
employee.

Article 19 - Application of Funds.
---------------------------------

     The proceeds received by the Company from the sale of Common Stock pursuant
to options granted under the Plan will be used for general corporate purposes.

Article 20 - Notice to Company of Disqualifying Disposition.
-----------------------------------------------------------

     By electing to participate in the Plan, each participant agrees to notify
the Company in writing immediately after the participant transfers Common Stock
acquired under the Plan, if such transfer occurs within two years after the
first business day of the Payment Period in which such Common Stock was
acquired. Each participant further agrees to provide any information about such
a transfer as may be requested by the Company or any subsidiary corporation in
order to assist it in complying with the tax laws. Such dispositions generally
are treated as "disqualifying dispositions" under Sections 421 and 424 of the
Code, which have certain tax consequences to participants and to the Company and
its participating subsidiaries.

Article 21 - Withholding of Additional Income Taxes.
---------------------------------------------------

     By electing to participate in the Plan, each participant acknowledges that
the Company and its participating subsidiaries are required to withhold taxes
with respect to the amounts deducted from the participant's compensation and
accumulated for the benefit of the participant under the Plan, and each
participant agrees that the Company and its participating subsidiaries may
deduct additional amounts from the participant's compensation, when amounts are
added to the participant's account, used to purchase Common Stock or refunded,
in order to satisfy such withholding obligations. Each participant further
acknowledges that when Common Stock is purchased under the Plan, the Company and
its participating subsidiaries may be required to withhold taxes with respect to
all or a portion of the difference between the fair market value of the Common
Stock purchased and its purchase price, and each participant agrees that such
taxes may be withheld from compensation otherwise payable to such participant.
It is intended that tax withholding will be accomplished in such a manner that
the full amount of payroll deductions elected by the participant under Article 7
will be used to purchase Common Stock. However, if amounts sufficient to satisfy
applicable tax withholding
<PAGE>

                                      -9-

obligations have not been withheld from compensation otherwise payable to any
participant, then, notwithstanding any other provision of the Plan, the Company
may withhold such taxes from the participant's accumulated payroll deductions
and apply the net amount to the purchase of Common Stock, unless the participant
pays to the Company, prior to the exercise date, an amount sufficient to satisfy
such withholding obligations. Each participant further acknowledges that the
Company and its participating subsidiaries may be required to withhold taxes in
connection with the disposition of stock acquired under the Plan and agrees that
the Company or any participating subsidiary may take whatever action it
considers appropriate to satisfy such withholding requirements, including
deducting from compensation otherwise payable to such participant an amount
sufficient to satisfy such withholding requirements or conditioning any
disposition of Common Stock by the participant upon the payment to the Company
or such subsidiary of an amount sufficient to satisfy such withholding
requirements.

Article 22 - Governmental Regulations.
-------------------------------------

     The Company's obligation to sell and deliver shares of Common Stock under
the Plan is subject to the approval of any governmental authority required in
connection with the authorization, issuance or sale of such shares.

     Government regulations may impose reporting or other obligations on the
Company with respect to the Plan. For example, the Company may be required to
identify shares of Common Stock issued under the Plan on its stock ownership
records and send tax information statements to employees and former employees
who transfer title to such shares.

Article 23 - Governing Law.
--------------------------

     The validity and construction of the Plan shall be governed by the laws of
the State of Delaware, without giving effect to the principles of conflicts of
law thereof.

Article 24 - Approval of Board of Directors and Stockholders of the Company.
---------------------------------------------------------------------------

     The Plan was adopted by the Board of Directors on December 9, 1999 and was
approved by the stockholders of the Company on January 20, 2000.

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