Ever heard of a guy called Newton? Well his wisdom has finally gotten used for somethin usefull.. The Game Magic Pen!
The shapes you draw are affected by three basic principles: gravity, friction, and inertia.
Use the mouse to draw an object.
You cannot draw inside other objects.
Draw a circle by holding the left mouse button.

You can use pins and hinges to link two objects together.
Hold S and click inside an object to draw a pin. Draw a second object on top of the pin to link the two object together.
Hold D to draw a hinge. It works the same as with a pin, except that now the two objects can rotate with respect to each other.

To erase a single object hold down A as you left click a shape.