[Mono] is an Open Source equivalent to .NET which is also compatible with the existing framework. In theory, the pieces you compile in either .NET or Mono should be interchangeable. Mono was originally created to enable .NET runtimes to run on Linux. And now there are Mono binaries for Windows and Linux. Mono 1.0 was officially released June 30,2004.... Rest of the story... [Compiling C# Win32 OpenGL Applications with Mono]