The all-star metal project of Dave Grohl where he played almost all the instruments (outside of lead parts by Bubba Dupree of Void, Kim Thayil of Soundgarden, and bass parts by Lemmy) that featured a multitude of vocalists. Dave recorded tracks reminiscent of the singers' respective bands, which he grew up greatly admiring, and sent the recordings to them, with a note stating simply "Send back with vocals."
Complete list of singers
Cronos (Venom) - "Centuries of Sin"
Max Cavalera (Soulfly, Nailbomb, Sepultura, Cavalera Conspiracy) - "Red War"
Lemmy Kilmister (Motörhead, Hawkwind) - "Shake Your Blood"
Mike Dean (Corrosion of Conformity) - "Access Babylon"
Kurt Brecht (D.R.I.) - "Silent Spring"
Lee Dorrian (Cathedral, Napalm Death) - "Ice Cold Man"
Scott 'Wino' Weinrich (Saint Vitus, The Obsessed, Spirit Caravan, The Hidden Hand) - "The Emerald Law"
Tom Gabriel Fischer (Apollyon Sun, Celtic Frost) - "Big Sky"
Snake (Voivod) - "Dictatorsaurus"
Eric Wagner (Trouble) - "My Tortured Soul"
King Diamond (King Diamond, Mercyful Fate) - "Sweet Dreams"
Jack Black (Tenacious D) - "I Am The Warlock" (hidden track, 8:56-12:08 of "Sweet Dreams")