Exhibit 10.1
                                                                    ------------

                                 PROMISSORY NOTE

$550,000.00                                                        June 20, 2000


     For  value  received,  the  undersigned, Charles J. Digate (the "Obligor"),
hereby  promises  to  pay  to  the  order  of  MathSoft,  Inc.,  a Massachusetts
corporation  (the  "Corporation"),  at  its principal office at 101 Main Street,
Cambridge,  MA  02142,  or at such other place as may be designated from time to
time  in  writing  by  the  Corporation, the principal sum of Five Hundred Fifty
Thousand  Dollars  and No Cents ($550,000.00) and interest at the rate of 8% per
annum  during  the initial period through June 19, 2002, and thereafter at a per
annum rate equal to the prime rate as announced from time to time by Fleet Bank.
Notwithstanding  any  other  provision of this Promissory Note (the "Note"), the
Corporation  does  not intend to charge and Obligor shall not be required to pay
any  interest  or  other  fees  or charges in excess of the maximum permitted by
applicable  law;  any  payments  in  excess of such maximum shall be refunded to
Obligor or credited to reduce principal hereunder.  All payments received by the
Corporation hereunder will be applied first to costs of collection, if any, then
to  interest and the balance to principal.  This Note shall be payable in lawful
money of the United States of America.  This Note is secured and entitled to the
benefits  of a Pledge Agreement between the Obligor and the Corporation dated as
of  the  date  hereof (the "Pledge Agreement") pursuant to which the Obligor has
pledged  securities  or collateral for one-half of the amount due and payable on
this  Note  at  any  time.

     Interest  shall be due and payable annually on each annual anniversary date
of this Note.  Interest shall be calculated on the basis of the actual number of
days  elapsed  over  a  year  of  360  days.

     From  and after June 19, 2002, this Note may be callable at any time by the
Corporation  and  shall  be  payable  within  five (5) days of the issuance of a
written  demand by the Corporation addressed to the address of the Obligor shown
on  the  signature page hereof; provided, however, that if the Obligor shall die
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at  any  time  prior  to the issuance of a written demand by the Corporation for
payment  or  the  occurrence  of any Event of Default, then the maturity date of
this Note shall become the fifth anniversary of the date of the Obligor's death.

     If  any day on which a payment is due pursuant to the terms of this Note is
not a day on which banks in the Commonwealth of Massachusetts are generally open
(a  "Business  Day"),  such  payment  shall  be  due  on  the next Business Day.

     This  Note may be prepaid at any time, without premium or penalty, in whole
or  in  part.  Any  prepayment of principal shall be accompanied by a payment of
accrued  interest  in  respect  of  the  principal  being  prepaid.

     This  Note or any portion hereof may, at the election of the holder of this
Note,  be  declared, without prior notice of any kind, to be immediately due and
payable  prior to and on or after June 19, 2002, upon or any time after the sale
of  275,000  shares  of  the  Corporation's  Common Stock or any portion thereof
issued  to  the Obligor on the date hereof upon partial exercise of that certain
Non-Qualified  Stock  Option  Agreement  between the Obligor and the Corporation
dated  as  of  September  9,  1994.


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     Upon  the  occurrence  of  any  Event  of  Default,  as  defined below, the
Corporation  may  declare any or all unpaid principal, accrued interest or other
amounts  payable  hereunder  from  Obligor  to  Corporation  immediately due and
payable  without  presentment,  demand,  protest  or  notice.

     "Event of Default" shall mean: (1) failure to pay any amount or perform any
obligation  as  set  forth herein or in the Pledge Agreement, which is not cured
within  thirty  (30)  days after written notice of such default from Corporation
(other  than the payment due five (5) days after the permissible demand therefor
by the Corporation); (2) insolvency (however evidenced) or the commission of any
act  of  insolvency;  (3)  the making of a general assignment for the benefit of
creditors;  (4) the filing of any petition or the commencement of any proceeding
by  Obligor  or any endorser of this Note for any relief under any bankruptcy or
insolvency  laws;  (5)  the  filing  of  any petition or the commencement of any
proceeding  against  Obligor  for  any relief under any bankruptcy or insolvency
laws,  which proceeding is not dismissed within sixty (60) days; or (6) the past
or  future making of a false representation or warranty by Obligor in connection
with  any  loan or loans by the Corporation, including as set forth in this Note
or  in  the  Pledge  Agreement.

     If this Note is not paid in accordance with its terms, Obligor shall pay to
Corporation upon its demand therefor, in addition to principal, accrued interest
and  other  amounts payable hereunder, all costs of collection of the principal,
accrued  interest,  and  such  other  amounts  including,  but  not  limited to,
reasonable  attorneys'  fees, court costs and other costs for the enforcement of
payment  of  this  Note.

     No  waiver  of any obligation of Obligor under this Note shall be effective
unless it is in a writing signed by Corporation.  A waiver by the Corporation of
any  right  or  remedy  under  this  Note  on any occasion shall not be a bar to
exercise  of the same right or remedy on any subsequent occasion or of any other
right  or  remedy  at  any  time.

     Any  notice  required  or permitted under this Note shall be in writing and
shall  be  deemed  to  have  been  given  on the date of delivery, if personally
delivered  to the party to whom notice is to be given, or on the second business
day  after  mail-ing,  if  mailed to the party to whom notice is to be given, by
certified  mail, return receipt requested, postage prepaid, or overnight courier
and addressed to the addressee at the address of the addressee set forth herein,
or  to the most recent address, specified by written notice, given to the sender
pursuant  to  this  paragraph.

     This  Note  is delivered in and shall be enforceable in accordance with the
laws  of the Commonwealth of Massachusetts, and shall be construed in accordance
therewith,  and  shall  have  the  effect  of  a  sealed  instrument.


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     Obligor hereby expressly waives presentment, demand, and protest, notice of
demand,  dishonor  and nonpayment of this Note, and all other notices or demands
of any kind in connection with the delivery, acceptance, performance, default or
enforcement  hereof,  and  hereby  consents  to  any delays, extensions of time,
renewals,  waivers  or  modifications that may be granted or consented to by the
holder hereof with respect to the time of payment or any other provision hereof.

     In  the  event any one or more of the provisions of this Note shall for any
reason  be  held to be invalid, illegal or unenforceable, in whole or in part or
in  any  respect, or in the event that any one or more of the provisions of this
Note operate or would prospectively operate to invalidate this Note, then and in
any  such  event, such provision(s) only shall be deemed null and void and shall
not affect any other provision of this Note and the remaining provisions of this
Note  shall remain operative and in full force and effect and in no way shall be
affected,  prejudiced,  or  disturbed  thereby.


Attested:                                   OBLIGOR:

By:  /s/  Dermot  P.  O'Grady               By:  /s/  Charles  J.  Digate
     ------------------------               ------------------------
Name:     Dermot  P.  O'Grady               Name:  Charles  J.  Digate
Title:    Chief  Financial  Officer


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