The Animus is the memory machine used in Assassin's Creed's modern-day storyline.
The device allows a user to access and experience genetic memories inherited from ancestors. In the first game, Abstergo uses the Animus to make Desmond Miles relive Altaïr's memories, turning historical events into a playable narrative.
The machine is a fictional technology based on the premise that memories can be encoded in DNA. Different versions appear throughout the series, and the Animus becomes important to both Abstergo's research and the Assassins' efforts to uncover information from the past.
The Helix is a later entertainment and research platform associated with Abstergo, not the original name of the memory machine. Eagle Vision is an Assassin ability, while an Apple of Eden is a Piece of Eden with a completely different function.