Crayon Physics is a simple yet astonishingly fun game. You have to move a circle in such a way that it collects a star in each of the seven levels. The only way to manipulate the circle is indirectly; you can, via using the mouse, draw objects that take the shape of squares or any type of rectangles and use these objects, for example, as a means to push the circle.
The simplest way is to just let a square appear above the circle and let if fall down on the circle. You can even build primitive swings and other objects. Aside from solving the main puzzle in each level it’s fun to just experiment, drawing objects and watching their interactions with each other and the environment.
Another neat side of the game is the style, the background looks like a real piece of paper and everything looks like it is drawn with crayon (hence the name). The only downside of the game is the limited nature of the objects you can make and that there are only seven very short levels.
But there’s already a sequel in development, Crayon Physics Deluxe, with a huge amount of levels, a level editor and the objects you can draw aren’t limited to just squares or rectangles.