Playful thinking
Rotate square sections of the grid to arrange the squares into numerical order starting from the top left.
In the basic game, you rotate a 2×2 square section. Left-click in the centre of that section (i.e. on a corner point between four squares) to rotate the whole section anticlockwise. Right-click to rotate the section clockwise. – Play the game here.
The game is part of an impressive game collection by Simon Tatham that you may play offline or online.
I wrote this collection because I thought there should be more small desktop toys available: little games you can pop up in a window and play for two or three minutes while you take a break from whatever else you were doing. And I was also annoyed that every time I found a good game on (say) Unix, it wasn’t available the next time I was sitting at a Windows machine, or vice versa; so I arranged that everything in my personal puzzle collection will happily run on both those platforms and more.