Microsoft Singularity - OS Research project
Singularity (OS)
Singularity (OS) is a Microsoft Research project started in 2003 to build a highly-dependable operating system in which the kernel, device drivers, and applications are all written in managed code (virtual OS).
The low-level x86 interrupt dispatch code is written in C & assembly language. 
Once this code has done its job, it calls the kernel, whose runtime & garbage collector are written in C# and run in unsafe mode. The hardware abstraction layer code is written in C++ and runs in safe mode. There is also some C code to handle debugging. The computer’s B.I.O.S. is only called during the 16-bit real-mode bootstrap stage; once in 32-bit mode, Singularity never calls the BIOS again, but rather calls device drivers written in C#. During installation, CIL (C Intermediate Language) opcodes of the C# kernel are compiled into x86 opcodes using the Bartok compiler. (wikipedia.org) ; Download Singularity Here.
