JaCIL (pronounced "jackal") is a project to create a byte-code compiler to translate .NET assemblies to Java class files.
NasmSharp is an open source effort to build a x86 assembler written in pure C#. Primarily it is a C# port of well known x86 assembler NASM, written in ANSI C. Involvement of some experienced C# programmers is highly appreciated.
Water: a fast, secure, dynamic OO language and database. Water is an all-purpose language (and meta-language) that runs Web applications in the browser or server-side. Water is compatible with .NET, Java, and C on Windows, Linux and Mac OS X system.