Here's a place where I'll dump my occasional crappy Processing prototypes. I usually make these to test some algorithmic idea for another game. They're open source!
Here's some:
Dotsworld 2 - cities send agents at each other and autonomously capture territory.
Flow Field - Just some particles in a predefined flow field.
Land Gen - Testing procedural terrain generation
Voxel Test - The thing which became DwarfCorp
2D Water - The thing which became DwarfCorp's water simulation
3D Water - The same thing as above, but in slices!
(Note: any of the openGL based ones will probably unfortunately not run in browser correctly.)