Game Genie
Slot your game into the Game Genie, slot the Game Genie into the console, thumb in a code from the booklet, and play with unlimited lives. Nintendo went to court to kill it, lost, and was ordered to pay Galoob the entire $15 million bond it had posted — a landmark copyright fight waged over a plastic cheat cart. It was never a Nintendo product, and it wasn't Nintendo-only: Sega gave the Genesis version its official approval while Nintendo was still in court.