Flow is a brilliant Flash game that's a sort of cross between Pac-Man and Nibbles, though that's hardly doing it justice. There's no plot to speak of, but you begin the game as a sort of small luminescent organism and you must eat other organisms to grow. You can go forward or back among the levels at will, but while the first levels are populated only by benign, easily-digestible prey, the later levels are filled with more dangerous adversaries that you'll only be able to defeat if you've out-evolved them. The game is unique in that there's no timer and no score display (your health is represented visually in the composition of your organism), and though there's a final goal (I won't spoil it for you), there's no real end to the game. Despite its simple premise and simple controls, Flow is a game that's satisfying to play and difficult to stop playing.