The best product that IBM made almost no money from. The PC is the longfather of all modern x86-based home computers, and the one that made the concept really catch on--if IBM is doing it, it must be right!
IBM first asked Gary Kildall for a variant of CP/M to run the PC, but he decided he'd rather fly his plane on the day they came by. The next guy on the list was named Bill Gates . . .