C# Operating System

I came across something called Cosmos and just thought it was very cool. It’s an operating system completely implemented in CIL compliant languages but especially focuses on C#. It seems like quite a cool idea to run this on especially small embedded devices but I’m left wondering what applications will be available that are compatible with the OS. I guess if they’ve implemented the .Net Base Libraries then they’ll be a fair amount already that will work but I haven’t looked at all at how this OS supports GUIs.