A simple particle system physics engine for processing. I've designed this to be application / domain agnostic. All this is supposed to do is let you make particles, apply forces and calculate the positions of particles over time in real-time. Anything else you need to handle yourself.
A. Walenstein. DSV-IS '02: Proceedings of the 9th International Workshop on Interactive Systems. Design, Specification, and Verification, page 133--147. London, UK, Springer-Verlag, (2002)