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Duik - Comprehensive animation and rigging toolset for Adobe After Effects
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Limber for After Effects - IK system for After Effects using shape layers as limbs for character animation
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Spine - Spine is 2D animation software designed specifically for software and game development.