A few years ago the music game business was booming beyond belief, but all good things must come to an end, and now those big plastic instruments are gathering dust in closets and corners. A casualty of that decline was Sing Hero, the games that would have followed in the legacy of Guitar Hero, Band Hero and DJ Hero if Activision hadn't cancelled it.
The trademark for Sing Hero was filed in 2009, and Pi Studios, which had previously ported Rock Band games to the Wii, had been enlisted to develop it. But Pi Studios doesn't exist anymore and the game will never see the light of day. These screenshots and concept art are all that remains of it, it seems.
It reportedly measured your score based on how many "fans" you had. And based on the screenshot above it seems it may have featured some first-person segments, changing the focus from the stage to the audience. Maybe.
We'll never know for sure, though we do know that there are probably enough karaoke games on the market without Sing Hero adding its voice to the chorus.