The remarkable Antikythera mechanism is a device more than 2000 years old apparently intended to compute the positions of the classical planets, predict eclipses, and perform related astronomical calculations.
The website of Britain's Guardian newspaper published an interesting article today that reports archaeologists will soon be re-visiting the site of the shipwreck where the mysterious device was found at the start of the 20th century. They're optimistic about making other interesting finds, because difficult diving conditions in the area have discouraged looting.
Here's a video clip about a reconstructed version of the mechanism that shows how it functioned:
A New York Times article from 2008 provides a lot of additional historical details about the device.