Tool are an alternative metal band formed in 1990 in Los Angeles, California. So far in their career they have won three Grammy Awards and achieved two Billboard chart topping albums. Their musical style is generally described as a mix of progressive rock, psychedelic rock and art rock.
Tool singer Maynard James Keenan and Serj Tankian have performed together as part of the Axis of Justice organisation. At a 2007 Tool gig in Auckland in New Zealand, Tankian was invited on stage to perform vocals on the song "Sober" (video: https://www.youtube.com/watch?v=Q9e1m2h9kms, Serj appears at 3:58)