Size Squared is a game built for iOS and Android devices. It's a simple game of timing screen taps to when a red square becomes approximately the same size as the base green square.
There are four different modes of play: easy, hard, harder, and hardest. In each mode, the player has 3 lives. If the red square grows a little bigger than the green square, you lose a life. A life is also lost if you tap too early. Each mode adds elements to the basic concept to really amp up the difficulty of the gameplay while still having a simple game.