Shift Me! is a classic 8-puzzle where you have to sort all stones in the right order. There are various levels (3x3, 4x4, 5x5 ... 10x10) and each level is missing one field to enable you to move other stones. The target of this puzzle is to solve in an efficient way. According to that you've a timer and a counter how much moves you've done.
It's suitable for here and there, so you can bypass time if you've to wait for something and simultaneously you can also train you brain.