Kepler's Orrery Lite is a gravity simulator that composes and plays
ambient music. In other words, it's a generative music system that uses gravity
equations as its driving force.

Each world starts with its own initial conditions, and then the
planets and gravity wells attract each other, swirl around, and
collide according to the laws of physics. Each world is different --
even changing the initial conditions a tiny bit makes the simulation
come out differently.

Then there's the music: each world plays its own "song," which changes
with every different simulation. Whenever a body hits something it
plays the next note on its melody. Each world has a different set of
melodies that play on different instruments. Some worlds make slow and
ambient music; others are random, sharp, and surprising.

You can play with the physics: change the gravitational constant; add
"antigravity" or friction; visualize the force fields and velocities.

You can also change the initial conditions of a world: with the world
editor, you can change the mass, positions and
velocities of the bodies and then restart the world to see how it
comes out different.

Turn on tilt gravity to let the real world influence the simulated
world.

Kepler's Orrery Lite is a free version of Kepler's Orrery. The free
version has fewer worlds and not as many soundbanks. For more worlds
and more varied sounds, upgrade to the full version.