Windows RT/Windows 8 API model

Windows RT only has the WinRT runtime and HTML5/Javascript engine. Windows 8 has both WinRT, CLR and Win32 APIs.

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.