Unity - The multiplatform game creation tools for everyone.
Synfig Studio - Just another WordPress site
Godot Engine - Feature-packed 2D and 3D open source game engine.
Duik - Comprehensive animation and rigging toolset for Adobe After Effects
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Limber for After Effects - IK system for After Effects using shape layers as limbs for character animation