The Hand In Hand clock is a fully functional software creation, where the minute hand rotates on the end of the hour hand, and the second hand rotates on the end of the minute hand. It's hard to read at first, but soon makes sense. The catch?

If my careful calculations are correct, the thing is fully extended at a different point each hour. Which means not only would a physical version of the Hand In Hand clock need to be mounted in the exact center of your wall, it would need a hell of a lot of room a full 360 degrees around in order to function without smacking into stuff. Unless of course you feel a titillating sense of mystery when the hands of your clock disappear behind a wardrobe, bookcase or framed portait. [Hand In Hand Clock in action, via Yanko via