Synfig Studio - Just another WordPress site
Spine - Spine is 2D animation software designed specifically for software and game development.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Animation Paper - Animation Paper is a software package for doing 2D animation.
Grafx2 - GrafX2 is a bitmap paint program inspired by the Amiga programs Deluxe Paint and Brilliance.
DigiCel FlipBook - Whether you do 2D, 3D or stop motion Animation, DigiCel FlipBook makes animation easier!