No mention of App Game Kit (AGK) here so let me fill in the gap. It's a mainly 2D cross platform SDK allowing you to code once in either C++ or it's own "Basic" language. Version 2 just got over 400% funding on Kickstarter and will have full 3D support, Spine support (for 2D animated characters), bullet physics and whole bunch of other new features.
It already has Facebook, Twitter, a bunch of Ultrabook sensor commands, Box2D and more. I've been using it from the start and love it (can you tell?). No, I don't work for The Game Creators (the company that created it) although I admit I did do for a while making some apps.
One of the best features from my point of view is you can develop on Windows and broadcast from the IDE over Wi-Fi to any supported device, so while I'm coding I can (within seconds) test my code on iPad, Android, Windows, Mac or Blackberry Playbook.
