There were lots of demos showing cross-platform Android / iOS and even OSX! (with MonoMac :). I met the creators of iCircuit and TouchDraw at MonkeySpace they

There were lots of demos showing cross-platform Android / iOS and even OSX! (with MonoMac :). I met the creators of iCircuit and TouchDraw at MonkeySpace they said it was really easy to get going and you just needed to design your library so the UI was decoupled from the main code-base (which you could effectively re-use as-is). Several of techniques of structuring your code-base was described in @gshackles talk, some of the slides are here: https://speakerdeck.com/u/gshackles/p/cross-platform-mobile-development-with-c-number-monkeyspace https://speakerdeck.com/u/gshackles/p/cross-platform-mobile-... (SpeakerDeck seems affected by EC2's outage). MonoGame (https://github.com/mono/MonoGame https://github.com/mono/MonoGame) is an implementation of XNA which allowed games like Bastion and Infinite Flight (A C# Flight Simulator) to run cross-platform.