[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….
Given that if you don’t have a copy of .NET or .NET 2003 you can compile with the “free” Mono compiler called “MCS”. MCS is a command line tool, so a typical project like [Triangle (My First OpenGL Program in C#] would use the following command line options to compile.
mcs Class1.cs CSharp.GLU.cs CSharp.OpenGL.cs CSharp.WGL.cs CSharp.Win32.cs
Just make Sure Mono is part of your path, typically the mono path is set to:
c:/Program Files/Mono-1.0/bin