Not a real game but a simple simulation of gravity in a solar system. Creates a number of random planets around a sun. Their number will decrease over time - they will collide, merge or fall into the sun. But in the end some will find a more or less stable orbit. I love watching it : )
Run the game to start the simulation. You can also adjust the camera:
Arrow keys to pan
LeftClick and drag to rotate
NumPlus/-Minus or PageUp/-Down to zoom
The code is in gravity.py and should be very easy to adjust if you're familiar with Python.
Cheers, have fun!