As mentioned Muvizu is one of a kind within this field as it offered actual 3D scenes, characters, and props. You can also import your own 3D elements into a scene. Motion tracking is easy, 3D camera operation, lip-syncing, and many more features. You don't have to be an animator to build your first scene in minutes.
Grit Game Engine - The Grit Game Engine is an MIT-Licensed Open Source Game Engine that is highly scriptable via Lua.
Plotagon - This app, Plotagon. is very fun. Creative and lets me express my ideas and all of my desiors!
Pygame - Pygame is a set of Python modules designed for writing games.
MocapX - Facial Motion capture app Maya and iPhone. With the MocapX animator, you can easily use the iPhone camera to animate characters in real time directly in Maya. MocapX tools enable you to use any custom or production rig as well as any Maya feature.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
FaceRig - FaceRig is a program that aims to enable anyone with a webcam to digitally embody awesome...