Mainsoft's Visual MainWin for J2EE licensed by Siebel Systems

Gartner ITxpo, San Diego, California - March 29, 2004 - Mainsoft^® Corporation, the cross-platform development company, today announced that Siebel Systems, Inc., a leading provider of business applications software, has licensed Visual MainWin^® for J2EE^TM . Siebel Systems' customers will use their large base of .NET developers to customize Siebel Systems' suite of CRM solutions for deployment on multiple .NET and J2EE platforms.

"It is very rewarding to work with Siebel Systems and other long-term customers to develop products that ensure critical cross-platform capabilities," said Yaacov Cohen, President and CEO of Mainsoft Corporation. "With Visual MainWin for J2EE, customers like Siebel Systems can empower their C# and .NET development teams to accelerate the development of J2EE enterprise applications."

Siebel Systems is committed to supporting both the J2EE and .NET environments. Its customers want the flexibility to deploy Siebel business applications on a variety of platforms and the ability to switch platforms over time as their business requirements change. Visual MainWin for J2EE allows Siebel Systems' customers to use C# and Visual Studio^® .NET (in addition to native Java) to write custom business logic that can be hosted natively on industry-standard J2EE application servers.

"We chose Mainsoft because it consistently delivers efficient development tools and methodologies for reducing time to market and application-creation costs, and Visual MainWin for J2EE is no exception," said Doug Smith, Vice President of Architecture, Siebel Systems.

Visual MainWin enables C# and Visual Basic .NET developers to create enterprise-class applications and Web Services for J2EE application servers from the Visual Studio.NET development environment. The product introduces a patent-pending ECMA-compliant C# compiler for J2EE that compiles the Microsoft Intermediate Language (MSIL) source code directly into standard Java byte code.

About Mainsoft Corporation

Founded in 1993, Mainsoft Corporation, the cross-platform development company, enables businesses to develop mission-critical applications with Visual Studio software and deploy them natively on J2EE, UNIX^® and Linux^® platforms, dramatically reducing development costs and time-to-market. The company is a first-mover in cross-platform development. Its world-class research and development team has created patented cross-platform products that solve critical problems facing independent software vendors (ISVs) and IT organizations. Many of the world's largest ISVs, including Siebel, Computer Associates and IBM Rational, use Mainsoft's products to extend the productivity of Microsoft Visual Studio, deploying more than $1 billion worth of software annually on multiple operating systems. Headquartered in San Jose, Calif., the company has 90 employees and offices in Chicago and Israel. For more information, visit www.mainsoft.com .

Contact Information:

Jenna Dobkin
415.652.2185
jennad@mainsoft.com

Mainsoft and MainWin are either registered trademarks or trademarks of Mainsoft Corporation. Microsoft, Visual Basic, Visual Studio, and Windows are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. Java and J2EE are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries. UNIX is a registered trademark of The Open Group.

Except for the historical information contained herein, this press release contains forward-looking statements that involve risk or uncertainties. Future operating results of Siebel Systems may differ from the results discussed or forecasted in the forward-looking statements due to factors that include, but are not limited to, risks associated with customer relations, such as the availability of Siebel Systems' products and services, customer implementation of products and services, relationships with customers, third-party vendors and systems integrators, concentration of revenues in a relatively small number of customers, existence of errors or defects in products, ability to successfully manage growth, significant current and expected additional competition and the need to continue to expand product distribution and services offerings. Further information on potential factors that could affect the financial results of Siebel Systems are included in Siebel Systems' Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and its other filings with the Securities and Exchange Commission, which are available at www.sec.gov . Siebel Systems assumes no obligation to update the information in this press release.

Siebel is a trademark of Siebel Systems, Inc. and may be registered in certain jurisdictions. All other product and company names mentioned are the property of their respective owners and are mentioned for identification purposes only.