I'm intrigued by Animata, an open source real-time animation program.
According to the website:
"The peculiarity of the software is that the animation - the movement of the puppets, the changes of the background - is generated in real-time, making continuous interaction possible. This ability also permits that physical sensors, cameras or other environmental variables can be attached to the animation of characters, creating a cartoon reacting to its environment. For example, it is quite simple to create a virtual puppet band reacting to live audio input, or set up a scene of drawn characters controlled by the movement of dancers."