From Microsoft :
"In addition to the CLI implementation and the C# compiler, the Shared Source CLI Implementation contains a cornucopia of tools, utilities, additional Framework classes, and samples. It will build and run on the Microsoft Windows® XP and the FreeBSD operating systems.
The Microsoft Shared Source CLI Implementation, affectionately known as "Rotor" to those of us on the team building it, is a complete implementation of the ECMA-334 (C#) and ECMA-335 (CLI) standards in source code form. It's an amazing piece of software for those who love browsing or tinkering with programming language infrastructure. In its million-plus lines of source code, you will find compilers, tools, techniques for automatically managing memory, just-in-time (JIT) code generators, component and Web services infrastructure, globalization know-how, security protocols, and all sorts of other intriguing realizations of abstract concepts. "
Some resources