I'm Nate, co-author of libgdx and many other OSS projects (Kryo, KryoNet, etc). I've been working on a game development tool with my good friend, Søren. I'm the programmer and he's the artist. The tool is called Spine and is used to build 2D skeletal animations specifically for games. We are doing a Kickstarter and passed our intial goal in just 3.5 days! We now have ~13 days left and we've just posted stretch goals, which include our plan for how to get Spine runtime support for almost all game toolkits.
You can see the Kickstarter here, and also a download link to try it now: http://www.kickstarter.com/projects/esotericsoftware/spine
Hopefully you like our tool and can take advantage of the ~50% off you get by obtaining a license before the Kickstarter is over. :)
Screenshot: http://esotericsoftware.com/spine/files/dragon-screenshot.jpg (the dragon project was provided by ODI EntertaintmenT http://www.odientertainment.com/ )