Wikipedia
pnetC is the Portable.NET C library. The goal of the project is to create an ANSI-compatible C library (based on GNU C Library - glibc), that can be compiled to IL using Portable.NET's "cscc" compiler. The C compiler can be used to develop standard C applications and/or applications using the .NET API.
The C compiler and library has been included with Portable.NET since version 0.4.4 and over time has matured enough to become a viable alternative to C# for writing Microsoft .NET applications. Although it is not yet feature complete, it does include a minimal standard C library and POSIX threads library, making it possible to develop complex applications. The C compiler generates pure CIL bytecode (with no dependencies upon external native libraries) and the ABI adapts itself to the particulars of the runtime engine that executes the program.