Xbox games are created by XNA .NET based framework.
But XNA is not ported to any other platform by Microsoft.
MonoGame is open source clone of XNA,
based on Mono, an open source clone of .NET.
MonoGame works on Android, iOS, Windows 8, Windows Phone 8...
ScottHa has interviewed developers of a popular game that is using MonoGame,
with 'code reuse' between mobile platforms of 95% !!
Even more interesting is that original animation is created in Flash,
and then converted in C#.
Before developing mobile game, original game was created for web in SVG and VML,
that was also converted from Flash... Real 'cool' technology...
Draw a Stickman Epic (Mobile)