It is Simon's task to try to get everyone out as quickly as possible, and it is every one else's job to stay 'in' for as long as possible. The last of Simon's followers to stay in wins (although the game is not always played all the way through). Until you try it, you can't understand how hard this can be.
Some closely related games are Mother May I (AKA Captain May I) and Ship Captain (AKA Port and Starboard).
Simon Says is a classic 1980s game more popularly known as Simon. It is a circular electronic game featuring four coloured quadrants. The game will flash quadrants in turn and expect you to repeat the sequence. If you get the sequence correct the game will respond with a longer sequence.