Algodoo

This is a trammel of Archimedes, also called an ellipsograph. The path of travel of the end of the arm draws a perfect ellipse, and they are often used to draw perfect ellipses. It is also known as a "do nothing device"/"do nothing grinder" when there is a handle attached to the end of the arm. You can either operate it with the drag tool, or turn the motor on in the axle settings.