Shifting puzzle
is an online jigsaw puzzle game, where the pieces can only be shifted
vertically or horizontally, column by column or row by row. It is however
guaranteed that the solution exists in all the cases presented to you.

Few mathematical knowledge is necessary in order to play
Shifting puzzle.
On the contrary, you can take a look on the exercise-game
Q-Puzzle to see how a jigsaw puzzle can require fairly deep mathematical concepts.