Swarm AI by Rob Kelly
based on Craig Reynolds's "Boids" flocking simulation - http://www.red3d.com/cwr/boids/
plus a few modifications of my own.
neat fact: Though the swarm behavior looks random, the simulation is actually entirely deterministic except for randomized starting positions and user input.
Controls: Left mouse to drag target, right mouse to spawn boids, - to remove target, z to remove boids, q to cycle quality
Source code: swarmAI