Simple SciPy implementation of a Newtonian n-body system. Can handle very complex systems in reasonable time. Produces pretty gifs too. :3
Figure it out. :P This isn't really designed to be super easily usable, as it's a random project I coded in a few hours, but it is reasonably powerful, using almost pure NumPy matrix implementation, and you can tweak whatever code you want in the original source. The plotting codebase is based on my Animator5D package.