go-llca is a life-like cellular automaton simulation tool written in Go. For the code and example simulations, see the Github page. Note that the browser version does not support exporting simulation runs as GIFs. For that, you can download the more performant native version from the Github releases page.

Fun rules to try include: B45678/S2345, B4678/S35678, B3578/S24678, B378/S245678.