BUILD: Windows Runtime – .winmd files
First off what is the Windows Runtime? Straight off Windows Dev Centre:
The .winmd files on Windows 8 are located at c:\Windows\System32\WinMetadata. If you first up .NET Reflector you can open the files are have a look at the WinRT types and classes, coupled with what the WinRT references itself – the CLR. Windows.System contains the Launcher that was shown in some of the BUILD keynote code if I remember correctly.