Mono

Mono is a software platform designed to allow developers to easily create cross platform applications.

It is an open source implementation of Microsoft's .Net Framework based on the ECMA standards for C# and the Common Language Runtime. Mono's C# compiler is feature complete for C# 1.0, 2.0, 3.0, and 4.0 (ECMA). The runtime implements the ECMA Common Language Infrastructure (CLI). The runtime provides a Just-in-Time (JIT) compiler, an Ahead-of-Time compiler (AOT), a library loader, the garbage collector, a threading system and interoperability functionality. The Mono platform provides a comprehensive set of classes that provide a solid foundation to build applications on. These classes are compatible with Microsoft's .Net Framework classes.