Magic Pen 2

Mouse and Left-Click = Draw Objects
Left-Click (Hold) = Draw Circle
(Hold) S and Left-Click inside an Object = Draw a Pin. (Draw a second object on top of the pin to link the two object together.)
(Hold) D and Left-Click = Draw a Hinge. (Works the same as with a pin, except that now the two objects can rotate with respect to each other.)
To Hold A and Left-Click a Shape = Erase a Single Object
Spacebar = Restart Level