It is called "Legends of Mata Nui."
It was supposed to be a computer game (I think) that had all of 2001's story from the Toa's point of view. It was scrapped, though, if I remember correctly, some prototype disks were put into some cereal boxes. You can only play Onua's level, since it ends on glitch that makes you unable to beat the game.
This is one of two scrapped BIONICLE games, the other being "Legends of Metru Nui."