Check this thing out! It's a mechanical rolling ball clock made from scratch.
From the video description:
The clock runs for 12 hours, driven by a weight of 2.5 kg sinking approx. 1 meter during that time. Every minute a marble is lifted up and goes down a marble run with three flipping traps that count marbles for minutes, five-minute-steps and hours. The timekeeping element is a second-pendulum with a pinwheel escapement. The clock achieves a drift of less than 1 second per day.
The clock is made of wood, some plastic gears, brass and steel wire, and an old flat iron. Here is where you can see stereoscopic photographs of the clock.
The clock is not unlike the Can You Imagine Time Machine Tabletop Clock. This clock has a battery-operated motor which lifts a steel ball bearing onto a concentric track at regular intervals. The ball then moves with others on a slow downward course, both halted and propelled by see-saws that tip when correctly weighted. The time can be read by observing the numerals that the balls are aligned with - hours and minutes are both indicated.
[ Thanks Christoph! ]