<PAGE>
 
                                                                    Exhibit 10.2

                                August 4, 1998



Dr. Alexander Stein
89 Robinson Road
Boxborough, MA  01719

Dear Dr. Stein:

     This letter agreement ("Agreement") sets forth the terms of your employment
with Gomez Advisors, Inc. ("Gomez Advisors" or the "Company"), a newly formed
and wholly owned subsidiary of Ashton Technology Group, Inc. ("Ashton").

     1.  Position/Responsibilities.  You will be employed as a Principal of the
         -------------------------                                             
Company. Your responsibilities will be as set forth by the President and CEO of
the Company.

     2.  Gomez Advisors.  Gomez Advisors will be engaged in the provision of
         --------------                                                     
strategic advice to financial services companies concerning the business
potential of the Internet as a tool for use in marketing and the interactive
distribution of financial products. Gomez Advisors will provide a range of
services including strategy development, marketing, product and interface
design, and implementation planning. You as a Principal of the Company will use
your best efforts to cause the Company to fulfill the foregoing objectives.

     3.  Term.  The term of your employment hereunder (the "Term") commenced on
         ----                                                                  
July 1, 1997 and shall continue until July 1, 2000 unless terminated earlier by
you or by the Company as provided below.

     4.  Base Salary and Benefits.  From the date hereof you shall be paid 
         ------------------------
a salary of $10,000 per month. At any time during the term of this Agreement,
your salary may be increased to a maximum of $15,000 per month at the discretion
of Mr. Julio Gomez based upon his own business judgment. You will be entitled to
the standard benefits as in effect from time to time for Gomez Advisors
executives commensurate with your position, a current schedule of which benefits
is attached hereto as Exhibit A. You will be entitled to twenty days of vacation
annually in addition to official Company holidays.

     5.  Expense Reimbursements.  The Company will reimburse you for all 
         ----------------------
reasonable business expenses you incur in fulfilling your responsibilities
hereunder upon submission of adequate documentation for such expenses and
subject to Company policies.

     6.  Termination/Severance Pay.  Either you or the Company shall have 
         -------------------------
the right to terminate your employment at any time with or without cause by
giving written notice to that 
<PAGE>
 
                                       2


effect. The termination of employment shall be effective on the prospective date
specified in such notice (the "Effective Termination Date").

     (i) If the Company terminates your employment without cause or if you
terminate your employment for "good reason," subject to the last sentence of
this paragraph, the Company will pay you as severance pay for a period beginning
on the Effective Termination Date and ending six months from such date (the
"Severance Period") your then current monthly salary (the "Salary"). The Salary
will be paid on the Company's normal payroll cycle during the Severance Period,
provided, that if you become employed elsewhere during the Severance Period the
amounts otherwise payable to you under this Section 6 (i) shall be reduced by
the total amount of any compensation you receive from such employment during the
Severance Period. For purposes of the severance pay offset provisions of this
Section, the terms "employed" and "employment" shall mean the providing of any
services for compensation whether as a full-time or part-time employee or as a
consultant or otherwise. In consideration of the severance pay herein provided
you agree to deliver to the Company on or promptly following the Effective
Termination Date a Separation and Release in the form used by the Company at
that time, subject to your agreement of the terms and conditions set forth
therein, provided, that in the event you do not deliver the Separation and
Release in the form then used by the Company your right to receive the severance
pay herein provided shall terminate. For purposes of this Agreement, "good
reason" shall mean Gomez Advisors' failure to perform in a timely manner its
material obligations under the Agreement, and shall not mean your removal from
your then current position with Gomez Advisors with your express written consent
or in connection with any termination of your employment by Gomez Advisors as
the result of your disability or "for cause."

     (ii) The Company shall have the right to terminate your employment for
cause by giving you written notice to that effect. The termination of employment
shall be effective on the date specified in such notice for that purpose.
"Cause" means (1) your failure to perform in a timely manner your material
obligations under this Agreement; (2) commission by you of a willful act of
dishonesty in the course of your duties with Gomez Advisors; (3) engagement by
you in negligence or conduct injurious to Gomez Advisors or its affiliates; (4)
your failure to comply with a written instruction from the Gomez Advisors Board
within your mandate as set forth herein; (5) your conviction of a crime of moral
turpitude or of a felony; or (6) your chronic alcoholism or drug abuse. If you
are terminated for cause, the Company will pay your unpaid Salary through the
effective date of the termination.

     7.  Death.  If you die during your employment hereunder, this Agreement 
         -----
shall terminate upon the date of your death. Thereafter, the Company shall pay
to the personal representative of your estate your unpaid Salary through the
date of death. Your estate shall also receive the benefit of any options that
are vested at the time of your death.

     8.  Options.  You are hereby granted a five-year option to purchase 75,000
         -------
shares of Common Stock of Ashton at an exercise price per share equal to the
closing market price of Common Stock of Ashton on September 2, 1997 (the "Ashton
Option").  The Ashton Option shall vest 33% on May 15, 1998, an additional 33%
on May 15, 1999 and the final 34% on May 15, 2000.  In the event of a change of
ownership control in Ashton prior to May 15, 2000, all 
<PAGE>
 
                                       3


unvested portions of the Ashton Option shall immediately and automatically vest.
You are also hereby granted a warrant to purchase 125,000 shares of Common Stock
of Universal Trading Technologies Corporation ("UTTC"), a subsidiary of Ashton,
at an exercise price of $1.00 per share (the "UTTC Warrant"). You may exercise
the UTTC Warrant at any time during the five-year period commencing on the
earlier of (a) September 30, 1999, (b) UTTC's first sale of Common Stock to the
public pursuant to a registration statement under the Securities Act of 1933, as
amended, which as been declared effective by the Securities and Exchange
Commission, other than a registration statement on Form S-8 or any similar form,
or (c) a sale of all or substantially all of the assets of UTTC.

     You are hereby granted "Founders'" options to purchase 750,000 shares of
Common Stock of Gomez Advisors at an exercise price per share of $0.01/share.
The Founders options are fully vested, may be exercised at any time, and will
expire on December 31, 2004. You are also hereby eligible to receive "Incentive"
options to purchase up to an additional 500,000 shares of Common Stock of Gomez
Advisors at an exercise price per share of $1.00/share and expire on December
31, 2004. The Incentive options shall be granted to you as follows: an option to
purchase 250,000 shares shall be granted immediately to you, and an option to
purchase an additional 250,000 shares shall be granted to you on July 15, 1999;
the date the registration statement for an initial public offering of Gomez
Advisors' Common Stock is declared effective; or a change in ownership control
of Gomez Advisors, whichever occurs first. Once granted by the Board, Incentive
options are fully vested, but may not be exercised by you until one year from
their grant or a change in ownership control of Gomez Advisors, whichever occurs
first.

     9.  Exclusivity.  In return for the compensation payments set forth in this
         -----------
agreement, you agree to devote substantially all of your professional time and
energies to Gomez Advisors.

     10.  Confidentiality.  In the course of your performance of your duties 
          ---------------
at Gomez Advisors, each of Ashton and Gomez Advisors will divulge to you certain
of its respective proprietary information, including, but not limited to,
information and data relating to or concerned with its business, finances and
other affairs. You agree that you will not divulge such proprietary information
to anyone at any time whether or not you are in the employ of Ashton and/or
Gomez Advisors, except as may otherwise be required in connection with the
business and affairs of Ashton or Gomez Advisors, as the case may be. You agree
to use your reasonable efforts to prevent such disclosure by others.

     11.  Assignment of Rights.  You agree that any inventions, developments,
          --------------------
discoveries, improvements, processes, methods, compositions, concepts, ideas or
inventions (whether or not patentable, or copyrightable or constituting trade
secrets or proprietary information) conceived, made, created, developed or
reduced to practice by you, alone or with others, during the Term and applicable
to the type of businesses engaged in by or any prospective activity of Ashton
and Gomez Advisors during such period (collectively, the "Intellectual
Property") shall be the sole and exclusive property of Gomez Advisors. By your
signature below you hereby assign all of your right, title and interest in the
Intellectual Property to Gomez Advisors and agree to execute and deliver all
documents requested by Gomez Advisors (including, without limitation,
applications for domestic or foreign patents, copyrights, or other proprietary
rights) to protect the 
<PAGE>
 
                                       4


respective rights of Gomez Advisors thereto. All copyrightable works that you
create during the Term shall be deemed "works made for hire."

     12.  Non-competition.  You further agree that during your employment 
          ---------------
with Gomez Advisors and for nine months after the termination of such employment
for any reason, you will not at any time engage in or participate as an officer,
employee, director, agent, consultant, representative, stockholder, investor or
partner, or have any financial interest, in any business which "competes" with
Ashton or any of its subsidiaries (other than Gomez Advisors) or successors. For
the purposes hereof, a "competing" business shall mean any business which
directly or potentially competes with any of the businesses of Ashton as such
business shall exist during your employment with Gomez Advisors, for example,
the development and commercialization of networked transaction systems for
participants in the financial markets of the type engaged in or contemplated by
Ashton or Gomez Advisors at the time of termination of your employment. For the
avoidance of doubt, a "competing" business shall not mean any business which
directly or potentially competes with the business of Gomez Advisors, which is
providing strategic advice to financial services companies regarding the
Internet or the interactive distribution of financial products. Ownership by you
of publicly traded stock of any corporation conducting any "competing" business
shall not be deemed a violation of this Section 12 provided you do not own more
than one percent (1%) of the stock of any such corporation.

     Additionally, for a period of nine months after the termination of your
employment hereunder you will not, directly or indirectly:

     (a) solicit or entice away from the Company or Ashton (i) the employment or
other services of any executive employee of Ashton or Gomez Advisors or (ii) the
business of either (A) any customer of Gomez Advisors to whom you rendered
services during the nine month period prior to your termination of employment (a
"Specific Customer"), or (B) any person or entity whose business you solicited
by multiple personal contacts during the nine month period prior to your
termination (a "Specific Contact"), or

     (b) participate in any activity for any Specific Customer or Specific
Contact which is the same as or substantially similar to those activities which
you performed for such Specific Customer or proposed to perform for such
Specific Contact, unless to do so would not have a material adverse effect on
the business conducted between Gomez Advisors and such Specific Customer or
Specific Contact.

     Further, for a period of nine months after the termination of your
employment hereunder you will not, directly or indirectly, hire any executive
employee of Ashton or Gomez Advisors.

     13.  Arbitration.  Disputes arising under or in any respect in connection  
          -----------
with this Agreement, including in respect of the execution, delivery or
performance hereof (but excluding disputes as to the compliance by the
arbitrators under the provisions of this Section applicable to them), shall be
arbitrated in New York City in accordance with the Commercial Arbitration Rules
of the American Arbitration Association by three arbitrators, one selected by
each party hereto and the third selected by the two so selected (or, in the
absence of agreement, the third arbitrator shall be selected by the President of
the Association of the Bar of The City of New 
<PAGE>
 
                                       5


York at the time sitting), and with all decisions of the arbitrators requiring
the affirmative vote of at least two of the arbitrators. Any judgment on any
award rendered by the arbitrators in accordance with such rules may be entered
in any court of competent jurisdiction. The parties intend to confer on the
arbitrators the authority to resolve disputes between the parties in respect of
this Agreement and agree that no decision by the arbitrators shall have the
effect of amending this Agreement in any respect. The costs of any such
arbitration, including expenses (and legal fees) of the other party thereto,
shall be borne by the party which is the losing party in the arbitration or, if
the arbitrators' decision is unclear in that regard, as the arbitrators shall
determine in accordance with the purpose of this provision to achieve the rules
that arbitrations be commenced hereunder in circumstances of actual disputes and
not frivolously or for harassment purposes. The parties hereto agree that any
proceedings pursuant to this Section 13 shall be kept strictly confidential and
shall not be disclosed to any third party except pursuant to court order.

     14.  Miscellaneous.  Together with the attached exhibits, this letter 
          -------------
agreement constitutes the entire understanding of the parties with respect to
the subject matter hereof and supersedes all prior agreements and
understandings, written or oral, among the parties with respect to such subject
manner. This Agreement is governed by the substantive laws of the State of New
York. This Agreement may be amended only in writing signed by both parties
hereto. This Agreement shall inure to the benefit of Gomez Advisors and any
successor of Gomez Advisors by reorganization, merger, consolidation or
liquidation, or any assignee or transferee of all or substantially all of the
business or assets of Gomez Advisors or of any division or line of business of
Gomez Advisors with which you are at any time associated. No provision of this
Agreement shall be for the benefit of or enforceable by any third party. Nothing
in this Agreement, expressed or implied, is intended to or shall be construed to
confer upon or to give any persons or party other than the parties hereto any
rights, remedies or claims under or by reason of this Agreement.

     Duplicate originals of this agreement are being provided to you.  Please
sign below to evidence your agreement to the foregoing, and return one original
for our records.

                                         Sincerely,


By:_________________                     By:_____________________
Julio Gomez                              Fredric W. Rittereiser
President and Chief Executive Officer    President and Chief Executive Officer
Gomez Advisors, Inc.                     Ashton Technology Group, Inc.


ACCEPTED AND AGREED


-------------------------
Alexander Stein

-------------------------
Date