This is a little physics engine I've been working on to show how planets and satellites accrete, flex under tidal forces, and orbit. There are a few different scenarios you can pick from right now. I plan to document this more later. Time step is in simulated seconds. Redraw interval determines how many iterations pass between graphics updates. You can set this to determine orbital and rotational periods. Set to 1 to see every frame. Pressing "print sim" will print out a JSON representation of the current simulation in the text box. The "load sim" button will read in and run whatever simulation is defined in the text box. If you save the contents of the text box in a file you can restore it later by copying it into the text box.
The red ball and "laser" coming out of it are just debugging aids for me until I don't need them. The red ball marks the center <0,0,0> of the coordinate system.