Spine - Spine is 2D animation software designed specifically for software and game development.
Synfig Studio - Just another WordPress site
FaceRig - FaceRig is a program that aims to enable anyone with a webcam to digitally embody awesome...
AnimeEffects - AnimeEffects is a 2D keyframe animation tool based on deformation of polygon meshes.
MocapX - Facial Motion capture app Maya and iPhone. With the MocapX animator, you can easily use the iPhone camera to animate characters in real time directly in Maya. MocapX tools enable you to use any custom or production rig as well as any Maya feature.
DragonBones - DragonBones is an open source project for 2D skeletal animation.