Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
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.
Synfig Studio - Just another WordPress site
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.
Unity 2D - Unity 2D is a powerful and feature-rich game design solution built from the ground up to fulfill every basic and advanced need of the developer.