Nine spheres hang together under gravity, each tuned to one note of a scale. It starts in D minor pentatonic; pick any other scale or key below. You stand on one of them. The music is whatever the spheres do to each other.
A sphere crossing the amber line in front of you plays its note. Higher in the sky bends the pitch up a step, lower bends it down.
Two spheres that touch strike together.
A close pass rings a bell.
Drag to look around. Tap a sphere to move onto it.
Now and then an asteroid falls in, tugs on the spheres and sometimes hits one.
Sound is positional and has a Doppler shift, so headphones help.