Fast ragdoll mechanics
Ragdoll Aquarium was an experiment in realistic character physics.
The applet can handle up to 300 simultaneous ragdolls at 60 fps on my laptop.
The same algorithms from Curtain are used for the physics in Ragdoll Aquarium. Thomas Jakobsen, the person who introduced the algorithm to game development in the game Hitman, originally used it for realistic character physics.
You can view the source and try the applet at OpenProcessing. Java is needed to run it.