A recent article from MSDN Magazine got my attention to this new operating system from Microsoft Research called Singularity.

Singularity is a new operating system, written almost entirely in C#, which executes only verifiably safe programs. Singularity's kernel and runtime libraries are the only parts of the system containing unsafe code and, even in those sections, most code is written in safe C#.

For more info you can read An Overview of the Singularity Project.