A game
The game is a grid of 5 by 5 buttons that can light up. Pressing a button
will switch its light around, but it will also switch the lights of the
adjacent buttons around. Each problem presents you with a
certain pattern of lit buttons and to solve the puzzle you have to turn
all the lights out (which is not easy because if you're not careful you
will turn more lights on than off). This is the primary goal, the
secondary goal is to accomplish this with as few moves (pressing a
button is one move) as possible.
Try it yourself on this grid. If a box has a check mark, this means its light is off.