I funded this awhile ago, and it was very relevant for a project I was working on, but if you guys are interested- the KickStarter has it discounted quite a bit:
I'm using it instead of flash for animating characters for my game, and it does a good job, as well as being lightweight.
Made by one of the two guys who are the main contributers of LibGDX.
Definitely more than worth it if you intend to ever use 2d skeletal animation in a project.
I spent a couple months writing a AIR program to convert flash XML files into easily read XML/JSON files, then loading them into my game, and it is still quite a ways off their app (That also includes the program to actually animate).
You can also buy it not off their website, but for a bit extra outside of the KickStarter(if you can't stand waiting 2 more days)