MusicBrainz is a community music metadatabase that attempts to create a comprehensive music information site. You can use the MusicBrainz data either by browsing this web site, or you can access the data from a client program — for example, a CD player program can use MusicBrainz to identify CDs and provide information about the CD, about the artist or about related information. You can also use the MusicBrainz Tagger to automatically identify and clean up the metadata tags in your digital music collections. ... More Info »
MusicBrainz is a user-maintained open community that collects, and makes available to the public, music metadata in the form of a relational database. MusicBrainz was initially created by Robert Kaye in response to Gracenote taking over the free CDDB project and charging people for access to the (what up till that point had been free) data. The MusicBrainz community has grown considerably since then, and the project has expanded its scope from being a CDDB replacement to a true "Wikipedia for music".
Additionally, freedb clients can access MusicBrainz data through the freedb protocol by using the MusicBrainz to FreeDB gateway (mb2freedb) service. It also very easy to import FreeDB entries into the MusicBrainz database (for missing CDs), by using MusicBrainz Picard 'manual lookup' functionality and then 'import freedb' on the relevant webpage.