Kepler's Orrery creates generative music based on a gravity simulator.
Start with a gravity simulator: bodies have mass, position, and velocity. They swirl around, attracted to everything else. When they collide, they light up, and occasionally play notes.
"Rocks" have mass but don't move. They're depicted as squares. You can grab them with the mouse and move them around.
Bodies bounce off the edge of the universe, but sometimes get stuck outside, until the "friction" slows them down enough to make their way back in.
Mutators randomly change the mass or velocity of things that collide with them. If a world has no mutators, it comes out the same each time (given the same) initial conditions.
When the world is finished playing, the stars wink out one by one, and eventually the notes stop.
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