Mono-Project

Mono provides the necessary software to develop and run .NET client and server applications on Linux, Solaris, Mac OS X, Windows, and Unix. Sponsored by Novell (http://www.novell.com), the Mono open source project has an active and enthusiastic contributing community and is positioned to become the leading choice for development of Linux applications.

Features:
    * Multi-platform.
    * Based on the ECMA/ISO standards.
    * Runs ASP.NET and Winforms applications.
    * Can run .NET, Java, Python and more.
    * Open Source, Free Software.
    * Commercially supported.
    * Comprehensive technology coverage.

Go to http://www.mono-project.com

See also these related projects.