This is a port of Daniel Shiffman's Reaction Diffusion coded in P5 (JavaScript): https://github.com/CodingTrain/Rainbow-Code/blob/master/CodingChallenges/CC_13_ReactionDiffusion_p5.js/sketch.js
Runs on my laptop at about 2-3 seconds per frame, so it takes an hour or more to get going. You can tweak the feed rate (FEED) and kill rate (K) to get radically different emergent patterns.
I may try to optimize it further (believe it or not, I have done some speedups to get it here) and maybe add a menu with some interesting pre-sets, but it is working, albeit very slowly.
Reaction Diffusion is similar to cellular automata like the Game of Life, but can create really amazing organic emergent patterns over time.