The theme is various fast ways to do large gravity simulations, but the main build artifact turned into kind of a "star simulator" (adding pressure alongside gravity) that renders videos like these in real-time: https://www.youtube.com/watch?v=DqYFIrdAAio I also played around with the Barnes-Hut algorithm, and a Walter Dehnen "O(n)" algorithm (https://arxiv.org/abs/astro-ph/0202512) which I struggled to understand :-) I ended up with a grid-based system, where acceleration from gravity is calculated at each cell using convolution, which is optimized with FFTs.