Unity was a shooter/music game by Jeff Minter/Llamasoft) in development for the Gamecube. It was cancelled in December 2004, after about two years work.
Unity was built concurrently with (or perhaps it's more accurate to say—on top of) Minter's Virtual Light Machine (VLM) 3, which would be later developed further into the XBox 360's visualiser Neon. The VLM was used to create the environments, and enemy patterns based on the game's soundtrack.
It was hinted at, via the Llamasoft forums, that Aphex Twin were set to be doing the music for the game. Or, maybe it was Underworld?
According to IGN's Unity page the game was to be released on '1 God', instead of the normal disc format. It was also to have Dualshock support.