When you're on the tube, waiting for the bus or queuing up in the supermarket. Any of these situations can be perfect to play Impossible Rush, a free Android game with which you can spend your free time and that has a really simple gameplay.
A game to play while you're waiting.
In Impossible Rush you have to rotate a cube made up by sides with different colors, so that the side matches the color of the ball that is being dropped at that precise moment.
A simple game that becomes frenetic
Controlling the game is very simple, as you only have to tap the screen to rotate it. The difficulty lies in the fact that the game pace becomes more and more frenetic, so you just might end up losing your patience (and the game).