Mono is an open source implementation of .NET Development Framework. Its
objective is to enable UNIX developers to build and deploy cross-platform
.NET Applications. The project implements various technologies developed by
Microsoft that have now been submitted to the ECMA for standardization.

Mono provides the necessary software to develop and run .NET client and
server applications on BSD, Linux, Solaris, Mac OS X, Windows, and Unix.

WWW: http://www.mono-project.com/