OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Synfig Studio - Just another WordPress site
Duik - Comprehensive animation and rigging toolset for Adobe After Effects
Adobe Animate - Adobe Animate is a Flash, vector 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.