Spine - Spine is 2D animation software designed specifically for software and game development.
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Synfig Studio - Just another WordPress site
Live2D Cubism - Live2D is the world's first drawing technology to enable 3D rendering of 2D images.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
AnimeEffects - AnimeEffects is a 2D keyframe animation tool based on deformation of polygon meshes.