This is a very cool game to test your ability to visualize shapes in a 3D environment. To quote the site, “The idea is to build up the solid shape indicated by the views to the left – but only using the number of cubes given. There are 10 problems, called figuur1 to figuur10. Be warned: they are not easy.”
I haven’t finished them all, but I’ve wasted enough time on it to know this is a pretty neat game.