The idea of the supergroup -- where members from different well-known bands come together to form another one -- is generally thought of as exclusive to classic rock, like Crosby, Stills, Nash & Young or Cream. But alternative and indie rock have more than their fair share, and we're recognizing some of the ones you may not remember in the above gallery of forgotten supergroups.

Temple of the Dog, the collaboration between half of Soundgarden and the group that would soon become famous as Pearl Jam, is arguably the best known of these, and Them Crooked Vultures, the Dave Grohl-Josh Homme-John Paul Jones project from 2009 isn't too far behind. But we're not interested in those right now.

Instead, these forgotten supergroups were usually the result of someone who had free time -- either the band broke up or went on hiatus or the musician got fired -- calling up some friends who had also some spare time on their hands for something new. So groups that have histories of frequent turnover (Red Hot Chili Peppers) or have taken several breaks (Jane's Addiction) are well-represented.

Some of these were intended to be one-offs, such as the time R.E.M. and Warren Zevon burned off some energy in the studio with a bunch of covers, or when six alternative rock stars pretended to be the early Beatles for a movie. Others didn't last longer than one night, like when half of R.E.M. merged with half of U2 to help welcome in a new president.

Click above to see what we came up with. Our list is bound to stir up some memories of these acts, and you can also find more bands devoted exclusively to grunge supergroups and collaborations here.