This is a good demo of how cellular automata don’t always have to look or behave like the Game of Life. Wireworld has four cell states—dead, wire, head, and tail—where dead cells stay dead; heads decay into tails, and tails into wires; wires become heads when excited by one or two heads; and wires stay wires otherwise. You can easily see how this gives rise to the “electrons on the subway” effect.<p>And in this system it’s fairly straightforward to actually build systems that compute things—albeit glacially slow. Contrast that with the Game of Life, where computation is more of an interesting emergent behaviour that’s about as easy as butterfly programming.