I just coded a small (less than 7 kb - assembler rulez!) program for windows that shows a small particles system algorithm. Very simple individual-based rules (move towards the neighboring particles, or fly away from them if there are too many) that give a very organic, but at the same time kind of chaotic, flocking behavior, like drunk mosquitoes flying around. You can change plenty of options on the fly. This code has no other purpose than being nice to watch. Please download it here and send bug reports or comments to me.