<PAGE>

                                                                   EXHIBIT 10.21

                                STOCK PLEDGE AGREEMENT


     THIS STOCK PLEDGE AGREEMENT is made as of February 3, 1998, between Joseph
Seebach ("Pledgor") and OneWave, Inc., a Massachusetts corporation ("Pledgee").

     Section 1. PLEDGE OF STOCK.  Pledgor hereby pledges, assigns, grants a 
first priority security interest in, and delivers to Pledgee the Stock (as 
hereinafter defined), to be held by Pledgee subject to the terms and 
conditions hereinafter set forth, the certificates for which, accompanied by 
stock powers or other appropriate instruments of assignment thereof duly 
executed by Pledgor, have been delivered to Pledgee.

     Section 2. DEFINITIONS.

          (a)  The term "STOCK" as used herein includes the shares of capital 
stock described in EXHIBIT A attached hereto and any additional shares of 
stock of any corporation or company at the time pledged with Pledgee 
hereunder.  The term "Stock" shall further include all cash or non-cash 
income from the shares of Stock pledged hereunder, all increases therein and 
proceeds thereof, other than income, increases or proceeds received by 
Pledgor pursuant to Section 6 hereof, and any dividend paid in respect of the 
Stock in the form of additional shares of stock, options to purchase stock, 
warrants or convertible securities (a "Non-Cash Dividend").

          (b)  The term "OBLIGATIONS" as used herein means all indebtedness, 
obligations and liabilities of Pledgor to Pledgee, whether now existing or 
hereafter arising, under that certain Promissory Note in the face amount of 
ONE HUNDRED AND FIFTY THOUSAND DOLLARS ($150,000) made by Pledgee in favor of 
Pledgor on February 3, 1998 (the "Note") and all future advances or loans 
given by Pledgee to Pledgor under any other arrangements.

          (c)  The term "Event of Default" as used herein shall mean the 
occurrence of an event of default under the Note.

     Section 3. SECURITY FOR OBLIGATIONS.  This Agreement and the pledge of 
the Stock hereunder is made in favor of Pledgee as security for the 
Obligations.

     Section 4. LIQUIDATION, RECAPITALIZATION, ETC.  Any sums paid upon or 
with respect to any of the Stock upon the liquidation or dissolution of the 
issuer thereof shall be paid over to Pledgee to be held by it as security for 
the Obligations; and in case any distribution of capital shall be made on or 
in respect of any of the Stock or any property shall be distributed upon or 
with respect to any of the Stock pursuant to the recapitalization or 
reclassification of the capital


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of the issuer thereof or pursuant to the reorganization thereof, the capital 
or property so distributed shall be delivered to Pledgee to be held by it as 
security for the Obligations.  All sums of money and property paid or 
distributed in respect of the Stock upon such a liquidation, dissolution, 
recapitalization or reclassification which are received by Pledgor shall, 
until paid or delivered to Pledgee, be held in trust for Pledgee as security 
for the Obligations.

     Section 5. WARRANTY OF TITLE.  Pledgor warrants that:  (a) Pledgor is 
the lawful, record and beneficial owner of the Stock; (b) the Stock is not 
subject to any pledge, lien, security interest, charge, option, restrictions 
or other encumbrances except the security interest created by this Agreement; 
(c) Pledgor has the power, authority and legal right to pledge all of such 
Stock pursuant to this Agreement; (d) no person has any present or future 
right (conditional, preemptive or otherwise) to acquire, vote, register or 
restrict the transfer of the Stock; and (d) the execution and delivery of 
this Agreement and the pledging of the Stock hereunder do not contravene any 
law or any rule or regulation thereunder or any judgment, decree or order of 
any tribunal, or conflict with, or result in a breach of or default under, or 
give a rise of acceleration under, any agreement or instrument to which 
Pledgor is a party or any of Pledgor's property is bound.

     Section 6. DIVIDENDS, VOTING, ETC., PRIOR TO MATURITY.  So long as no 
Event of Default has occurred and is continuing, Pledgor shall be entitled to 
receive all cash dividends paid in respect of the Stock, to vote the Stock 
and to give consents, waivers and ratifications in respect of the Stock, 
PROVIDED that no vote shall be cast, or consent, waiver or ratification given 
or action taken which would be inconsistent with or violate any provisions of 
this Agreement, and PROVIDED FURTHER, that upon an Event of Default, Pledgee 
may cause the Stock to be transferred into its own name as collateral 
security. All such rights of Pledgor to receive cash dividends shall cease in 
case an Event of Default shall have occurred and be continuing.  All such 
rights of Pledgor to vote and give consents, waivers and ratifications with 
respect to the Stock shall, at Pledgee's option, as evidenced by Pledgee 
notifying Pledgor of such election, cease in case an Event of Default shall 
have occurred and be continuing.  In the event that a Non-Cash Dividend shall 
be paid in respect of the Stock, Pledgor shall promptly deliver to Pledgee 
the certificates issued in connection with such Non-Cash Dividend, if any, 
together with stock powers or other appropriate instruments of assignment 
thereof duly executed by Pledgor.

     Section 7. REMEDIES.  If an Event of Default shall have occurred and be 
continuing, Pledgee shall thereafter have the following rights and remedies 
(to the extent permitted by applicable law) in addition to the rights and 
remedies of a secured party under the Uniform Commercial Code of 
Massachusetts, all such rights and remedies being cumulative, not exclusive, 
and enforceable alternatively, successively or concurrently, at such time or 
times as Pledgee deems expedient:


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          (a)  if Pledgee so elects and gives notice of such election to
Pledgor, Pledgee may vote any or all shares of the Stock and give all consents,
waivers and ratifications in respect of the Stock and otherwise act with respect
thereto as though it were the outright owner thereof (Pledgor hereby irrevocably
constituting and appointing Pledgee the proxy and attorney-in-fact of Pledgor,
with full power of substitution, to do so);

          (b)  Pledgee may demand, sue for, collect or make any compromise or
settlement Pledgee deems suitable in respect of the Stock;

          (c)  Pledgee may sell, resell, assign and deliver, or otherwise
dispose of any or all of the Stock, for cash and/or credit and upon such terms
at such place or places and at such time or times and to such persons, firms,
companies or corporations as Pledgee thinks expedient, all without demand for
performance by Pledgor or any notice or advertisement whatsoever except such as
may be required by law; and

          (d)  Pledgee may cause all or any part of the Stock held by it to be
transferred into its name or the name of its nominee or nominees.

     Pledgee may enforce its rights hereunder without any other notice and 
without compliance with any other condition precedent now or hereunder 
imposed by statute, rule of law or otherwise (all of which are hereby 
expressly waived by Pledgor, to the fullest extent permitted by law).  
Pledgor acknowledges that ten (10) calendar days' notice of any public sale 
or of that date on or after which a private sale may be effected is 
reasonable notice.  Pledgee may buy any part or all of the Stock at any 
public sale, and if any part or all of the Stock is of a type customarily 
sold in a recognized market or is of the type which is the subject of 
widely-distributed standard price quotations, Pledgee may buy at a private 
sale and may make payments thereof by any means.  Pledgee may apply the cash 
proceeds actually received from any sale or other disposition of the Stock to 
the reasonable expenses of retaking, holding, preparing for sale, selling and 
the like, to reasonable attorneys' fees, and all legal expenses, travel and 
other expenses which may be incurred by Pledgee in attempting to collect the 
Obligations or to enforce this Agreement or in the prosecution or defense of 
any action or proceeding related to the subject matter of this Agreement; and 
then to the Obligations, and any surplus shall be paid to Pledgor.

     Pledgor recognizes that Pledgee may be unable to effect a public sale of 
the Stock by reason of certain prohibitions contained in the Securities Act 
of 1933, as amended, but may be compelled to resort to one or more private 
sales thereof to a restricted group of purchasers or to a public sale which 
is restricted to residents of the Commonwealth of Massachusetts.  Pledgor 
agrees that any such private sales or such restricted public sales may be at 
prices and other terms less favorable to the seller than if sold at public 
sales and that such private sales or such restricted public sales shall not 
by reason thereof be deemed not to have been made in a


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commercially reasonable manner.  Pledgee shall be under no obligation to 
delay a sale of any of the Stock for the period of time necessary to permit 
the issuer of such securities to register such securities for public sale 
under the Securities Act of 1933, as amended, even if the issuer would agree 
to do so.

In all events, Pledgee shall give Pledgor not less than ten (10) calendar 
days' written notice of any proposed disposition of the Stock.

     Section 8. MARSHALLING.  Pledgee shall not be required to marshal any 
present or future security for (including but not limited to this Agreement 
and the Stock pledged hereunder), or guarantees of, the Obligations, or to 
resort to such security or guarantees in any particular order; and all of its 
rights hereunder and in respect of such security and guarantees shall be 
cumulative and in addition to all other rights, however existing or arising.  
To the extent that he lawfully may, Pledgor hereby agrees that he will not 
invoke any law relating to the marshalling of collateral which might cause 
delay in or impede the enforcement of Pledgee's rights under this Agreement 
or under any other instrument evidencing any of the Obligations or under 
which any of the Obligations is outstanding or by which any of the 
Obligations is secured or guaranteed, and to the extent that it lawfully may 
Pledgor hereby irrevocably waives the benefits of all such laws.

     Section 9. PLEDGOR'S OBLIGATIONS NOT AFFECTED.  The obligations of Pledgor
hereunder shall remain in full force and effect without regard to, and shall not
be impaired by: (a) any bankruptcy, insolvency, reorganization, arrangement,
readjustment, composition, liquidation or the like of Pledgee; (b) any exercise
or nonexercise, or any waiver, by Pledgee of any right, remedy, power or
privilege under or in respect of the Obligations or any of any security therefor
(including this Agreement); (c) any amendment to or modification of any
instrument (other than this Agreement) securing any of the Obligations; or (d)
the taking of additional security for, or any guaranty of, any of the
Obligations or the release or discharge or termination of any security or
guaranty for any of the Obligations; whether or not Pledgor shall have notice or
knowledge of any of the foregoing.

    Section 10. TRANSFER, ETC., BY PLEDGOR.  Without the prior written 
consent of Pledgee, Pledgor will not sell, assign, transfer or otherwise 
dispose of, grant any option with respect to, or pledge or grant any security
interest in or otherwise encumber any of the Stock or any interest therein, 
except for the pledge thereof provided for in this Agreement.

   Section 11.  FURTHER ASSURANCES.  Pledgor will, from time to time, execute 
and deliver to Pledgee all such other and further instruments and documents 
and take or cause to be taken all such other and further action as Pledgee 
may reasonably request in order to effect and confirm more securely in 
Pledgee all rights contemplated in this Agreement.


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   Section 12.  PLEDGEE'S EXONERATION.  Under no circumstances shall Pledgee 
be deemed to assume any responsibility for or obligation or duty with respect 
to the Stock or any matter or proceedings arising out of or relating thereto, 
other than to exercise reasonable care in the physical custody of the Stock.  
Pledgee shall not be required to take any action of any kind to collect, 
preserve or protect its or Pledgor's rights in the Stock or against other 
parties thereto, other than to exercise reasonable care in the physical 
custody of the Stock.

   Section 13.  NO WAIVER, ETC.  No act, failure or delay by Pledgee shall 
constitute a waiver of its rights and remedies hereunder or otherwise.  No 
single or partial waiver by Pledgee of any default or right or remedy which 
it may have shall operate as a waiver of any other default, right or remedy 
or of the same default, right or remedy on a future occasion.  Pledgor hereby 
waives presentment, notice of dishonor and protest of all instruments, 
included in or evidencing any of the Obligations, and any and all other 
notices and demands whatsoever (except as expressly provided herein).

   Section 14.  NOTICE, ETC.  All communications herein provided shall be in 
writing and shall be sufficient if sent by United States mail, registered or 
certified, postage prepaid, delivered by messenger, overnight delivery 
service or telecopier, addressed as follows:

          If to Pledgor, at the address set forth below Pledgor's signature.
     
          If to Pledgee:      OneWave, Inc.
                              One Arsenal Marketplace, 2nd Floor
                              Watertown, MA 02172
                              Telecopier:  (617) 923-6565
                              Attention:  Chief Financial Officer

or to such other address as the party to receive any such communication or
notice may have designated by written notice to the other party.

     Any notice given pursuant to this Section shall be deemed to have been
given and received when actually delivered, upon receipt of electronic
confirmation if by telecopier, one business day after dispatch by a recognized
overnight delivery service, or three business days after mailing by certified or
registered mail with proper postage affixed and return receipt requested.

   Section 15.  TERMINATION.  This Agreement shall terminate at such time as 
all of the Obligations shall have been paid in full, and upon such 
termination, Pledgor shall be entitled to the return of such Stock in the 
possession or control of Pledgee as has not theretofore been disposed of 
pursuant to the provisions hereof and as to which Pledgee has not received 
notice


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of a junior pledge, together with any moneys and other property of Pledgor at
the time held by Pledgee hereunder.

   Section 16.  MISCELLANEOUS PROVISIONS.  

          (a)  Neither this Agreement nor any term hereof may be changed,
waived, discharged or terminated except by a written instrument expressly
referring to this Agreement and to the provisions so modified or limited, and
executed by the party to be charged.  

          (b)  This Agreement is personal and may not be assigned by Pledgor. 
This Agreement and all obligations of Pledgor hereunder shall be binding upon
his heirs, executors and administrators.  Pledgee shall have the right to assign
this Agreement, without any restriction, and Pledgee's rights and remedies under
this Agreement shall inure to the benefit of its assigns and successors by way
of merger, consolidation or sale of substantially all of the assets or stock of
Pledgee.  

          (c)  This Agreement and the obligations of Pledgor hereunder shall be
governed by and construed in accordance with the laws of The Commonwealth of
Massachusetts.

          (d)  The descriptive section headings have been inserted for
convenience of reference only and do not define or limit the provisions hereof. 
If any term of this Agreement shall be held to be invalid, illegal or
unenforceable, the validity of all other terms hereof shall be in no way
affected thereby, and this Agreement shall be construed and be enforceable as if
such invalid, illegal or unenforceable term had not been included herein. 

          (e)  This Agreement may be executed in counterparts, each of which
shall be deemed an original and all of which together shall be deemed to be one
and the same instrument.

          (f)  To the extent permitted by applicable law, Pledgor hereby waives
trial by jury in any proceeding brought for the interpretation or enforcement of
this Agreement or for a determination of the rights of the parties hereunder.

   Section 17.  CONSENT TO JURISDICTION.  PLEDGOR AND PLEDGEE IRREVOCABLY 
CONSENT AND SUBMIT TO THE JURISDICTION OF THE UNITED STATES DISTRICT COURT 
FOR THE DISTRICT OF MASSACHUSETTS, AND THE COURTS OF THE COMMONWEALTH OF 
MASSACHUSETTS IN CONNECTION WITH ANY ACTION, PROCEEDING OR CLAIM ARISING OUT 
OF OR RELATING TO THIS AGREEMENT AND/OR ANY INSTRUMENT OR DOCUMENT REQUIRED 
HEREBY OR INCIDENT OR COLLATERAL HERETO.


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     IN WITNESS WHEREOF, Pledgor and Pledgee have caused this Agreement to be
duly executed as of the date first above written.

                              "PLEDGOR"

                              /s/ Joseph Seebach
                              ------------------------------------
                              Joseph Seebach

                    Address:  8 Country Squire Dr.
                              ------------------------------------
                              Norfolk, MA 02056
                              ------------------------------------

                              "PLEDGEE"

                              ONEWAVE, INC.


                              By: /s/ Lennart Mengwall
                                  ---------------------------------
                                  Name:   Lennart Mengwall
                                  Title:  President

SPOUSE'S CONSENT:

I, as the spouse of Joseph Seebach, 
acknowledge that I have read the 
foregoing Stock Pledge Agreement, 
that I understand the contents thereof,
and that I hereby waive any and all 
rights to the Stock described therein, 
to the extent such rights conflict with 
rights of Pledgee thereunder.


_________________________
Name:


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                                      EXHIBIT A


<TABLE>
<CAPTION>
Issuer         Class of Stock      Certificate Number       Number of Shares
------         --------------      ------------------       ----------------
<S>            <C>                 <C>                      <C>
OneWave, Inc.  Common Stock             ________                 100,000
</TABLE>





DOCSC\592817.1