Bionicle: Legend of Mata Nui is a cancelled PC game based on the Lego Bionicle franchise, that was in development at the Lego Software division. The project was officially cancelled in 2001, because of some quality issues and too many delays. It seems that a playable beta demo does exist somewhere out there.
Thanks to Lord Deathsaur for the contribution! You can find some more infos on the game at the Mask of Destiy website.