Simple Simon

Play the game here: Simon

It's easy - all you have to do is repeat what Simon says. 

There are four colors: blue, green, red, and yellow. Simon will choose a random color, "light up" that button, then give you a chance to copy what he did. Once you do, Simon will repeat his sequence and add a random move. If you successfully copy what he did, he'll add another, and another, and another. The game ends when you make a move that wasn't in Simon's sequence, but he'll ask if you want to play again.