This Clock Uses Gravity Instead of a Mainspring

A gravity clock slowly rolls down an inclined plane. The turning motion powers the clock. To reset it, move it back to the top of the platform. Physics Fun explains:

As the clock rolls down the incline (here 12 hours are captured in time-lapse of 24 seconds), gravitational potential energy is translated into the kinetic energy of the moving clock gear train and oscillating balance wheel. The clock face and mechanism hang suspended with a counterweight that keeps them upright- although you might notice the mechanism of this vintage clock sticks a little at 7 o’clock. The clock unit is also quite heavy, weighing in at 2.7kg (6lbs). After some research I believe this clock was produced in China about 50 years ago. 

-via reddit