Click or drag on the grid to draw cells. The edges wrap around. The address of the page keeps the rule, to share it.
Birth and survival
In 1970 the mathematician John Conway invented a game with no players. A grid of cells, each alive or dead; at every tick, each cell counts its eight neighbors. A dead cell with exactly three live neighbors is born. A live cell with two or three survives. All others die, of loneliness or overcrowding. Martin Gardner described it in Scientific American, and people started running it on every computer they could find.
Out of those two rules come still lifes, blinkers, and the glider, a five-cell shape that walks across the grid. Bill Gosper found a gun that fires gliders forever, which proved that Life can grow without end; later, people built logic gates, counters, and a whole computer out of gliders.
Write the rule as B3/S23: born with 3 neighbors,
survives with 2 or 3. Change the numbers and you get other worlds:
B36/S23 (HighLife) has a pattern that copies itself,
B3/S12345 grows mazes, B1357/S1357
replicates anything. A third number gives the cells dying states,
as in Brian Silverman's Brian's Brain,
B2/S/3: a cell that fires is spent for a tick, and
sparks race across the grid forever.