Windows RT/Windows 8 API model
WinRT can be targetted by C#, C++.
CLR is .NET which means C++, C#, VB.NET, JScript.NET, IronPyton, IronRuby, F#
Win32 is C++
Applications written against WinRT API are to be submitted to the Windows app store and Microsoft will automatically compile it to ARM & x86 binaries.
Surface RT is an ARM-only tablet that runs WinRT & HTML5/JS.
Surface Pro is an x86 tablet which runs WinRT, HTML5/JS, CLR and Win32.