Built this afternoon with an array, a canvas, and one huuuuuuge for loop. There's probably a better, more efficient way to do this, but as far as I can tell, this obeys all of the rules of Conway's Life.
.cap included for those interested. If you want a random field generator, untoggle the first event and right click when the game opens.
Left click places a punnet (on a 50*50 unmarked grid) and right click starts the simulation (can't pause or add new punnets after that).