To clarify, part of what makes this possible is that they extended C# with some attributes to specify that regions of code should run in a sort of high-integrity mode, where they can't be suspended for GC, etc. This allows them to do things like handle interrupts safely from C#. They call it 'Constrained Execution Regions'.

http://msdn.microsoft.com/en-us/library/ms228973.aspx

Cosmos is more interesting. It is a toolkit to create operating systems in C# - http://en.wikipedia.org/wiki/Cosmos_(operating_system)

Looking verbatim at the starting question, it's stll not comparable to Windows 7, in a sense of all built-in functionality in Windows 7. But it is a nice and smart research project.