Spine - Spine is 2D animation software designed specifically for software and game development.
Synfig Studio - Just another WordPress site
Animation Paper - Animation Paper is a software package for doing 2D animation.
Live2D Cubism - Live2D is the world's first drawing technology to enable 3D rendering of 2D images.
CrazyTalk Animator - CrazyTalk Animator, the next level of 2D animation. Create actors using any photo or illustration.
AnimeEffects - AnimeEffects is a 2D keyframe animation tool based on deformation of polygon meshes.