Cellular automata
A grid of cells that obey two rules. Every cell has 8 neighbours - up, down, left, right and diagonals. A dead cell becomes alive if the number of its living neighbours is one of the numbers in the birth rule, and a living cell stays alive if the number of its living neighbours is one of the numbers in the survival rule (otherwise it dies).
You can click on the numbers to change the rules. If you find something interesting, you can use this kind of notation and search for it: B5678/S45678. By searching that I learned that this particular one is called the Vote rule. Conway's Game of Life has the rule B3/S23.
This was a little experiment with Zig and WebAssembly. The font is from damieng, who has made loads of great bitmap fonts.