Singularity is a Microsoft Research project started in 2003 to build a highly-dependable operating system which mean Kernel, Drivers and Applications written in managed code using C# and C# extra extensions.
Questions might arise in our minds: Is it possible that Microsoft will replace Windows with Singularity? What make it different from Windows? Is because it was build from scratch or have more to offer than Windows?
Any way you could try it but be careful it is classified under research and don't expect Windows like graphics.
Official home page