Synfig Studio - Just another WordPress site
Duik - Comprehensive animation and rigging toolset for Adobe After Effects
Animation Paper - Animation Paper is a software package for doing 2D animation.
Limber for After Effects - IK system for After Effects using shape layers as limbs for character animation
CrazyTalk Animator - CrazyTalk Animator, the next level of 2D animation. Create actors using any photo or illustration.
Spine - Spine is 2D animation software designed specifically for software and game development.