What is the apple of Edin in the assassins creed series

The Apple of Eden is a device that has special powers i.e; make copies of yourself or others and they follow your exact commands which you can see on the last level of Assassin's Creed 1 & 2. There are lots of other objects called the 'Pieces of Eden' like the Staff of Eden that you see aswell in the end of Assassin's Creed 2 and the Sword of Eden which is supposed to be Excalibur from the 'Tales of King Arthur & Camelot' but has not yet been seen in the series.