Astronomer Phil Plait is excited about this (and so am I because it figures in the new book proposal I’m trying to sell right now):

The Antikythera Mechanism is an artifact found on a sunken boat a century ago. It’s a device that has bronze gears and apparently was used to do some sort of calculation… by ancient Greeks, because it’s about 2000 years old.

Its specific function has always been a mystery because of the deteriorated condition of the device, but new techniques (including advanced X-ray imaging) have revealed writing on the back side of the mechanism, indicating it was used as an astronomical tool. The names of the 12 months are inscribed, and other markings indicate it was used to predict solar eclipses and the timing of the four-year Olympiad.