Musicbrainz

MusicBrainz is a community-maintained open source encyclopedia of music information.
MusicBrainz was founded by Robert Kaye in 2000 as a response to Gracenote taking over the free CDDB project and commercializing it, essentially charging users for access to the very data they had contributed themselves. The project rapidly grew from a one-man operation to a large community of like-minded people, expanding its scope along the way from being merely a CDDB replacement to being a true Wikipedia for music!