TinyTris

TinyTris does one thing, and it does it pretty well: It clones the GameBoy version of Tetris. (Specifically the "A-type" mode which is the one I think people most commonly play.) I assume you've played Tetris before, and the game is the same here; four-block shapes fall down a well, and you must arrange them to form complete horizontal lines which are then cleared from the playing field. Graphically, the game looks quite similar to the GameBoy edition, with the same colors. The speed of the game increases as you complete more and more lines.