During an era of music game over indulgence, Activision was planning on releasing Sing Hero, a karaoke version of the popular (but overcrowded), Hero series.
Thanks in large part to the music game genre dying an incredibly quick death (thanks in larger part to Activision's own market flooding), Sing Hero never saw the light of day. Siliconera managed to get its hands on some of Pi Studios' concept art for the game that never was, revealing an eclectic group of male and female avatars emulating several of the biggest music stars at the time.
Details on just what the game would have been like are slim, though Sing Hero reportedly would have tracked the number of fans a player earned as their score. Obviously a track listing is too much to have hoped for, but judging by the faux Katy Perry, Avril Lavigne, and Justin Timberlake, you can get an idea of just what kind of tunes you'd have been belting out.
A straight-up karaoke game not requiring numerous peripherals could have managed to be a success, but since Sing Hero has been abandoned, we'll likely never know what could have been.