What is the Antikythera mechanism? Is this the world's first computer?

Google's Doodle is celebrating the Antikythera mechanism, which might just be the first computer. The mechanism was found in 1902 – exactly 115 years ago – and the discovery changed the way we saw the ancient Greeks. The man who found it, Valerios Stais, initially thought that the bronze mechanism he could see was a gear or a wheel – but on closer inspection, the metal turned out to be part of the Antikythera mechanism, an ancient and mysterious analogue astronomical computer. The machine could be used to track and predict where the planets were, understand lunar and solar eclipses, and count towards the next Olympic Games. But its uses were various – it might also have been used for unknown forms of mapping and navigation.