FreeDB

freedb is a database of compact disc track listings, where all the content is under the GNU General Public License. To look up CD information over the Internet, a client program calculates a hash function from the and uses it as a disc ID to query the database. If the disc is in the database, the client is able to retrieve and display the artist, album title, track list and some additional information.

It was originally based on the now-proprietary CDDB (Compact Disc DataBase). Because it inherited the CDDB limitations, there is no data field in the freedb database for composer. This limits its usefulness for classical music CDs. Furthermore, CDs in a series are often introduced in the database by different people, resulting in inconsistent spelling and naming conventions across discs. As of April 24, 2006, the database held just under 2,000,000 CDs. As of 2007, MusicBrainz – a project with similar goals – had a freedb gateway that allows access to their own database.

The original software behind CDDB was released under the GNU General Public License, and many people submitted CD information thinking the service would also remain free. The license was later changed, however, and some programmers complained that the new license included certain terms that they couldn't accept: if one wanted to access CDDB, one was not allowed to access any other CDDB-like database (such as freedb), and any programs using a CDDB lookup had to display a CDDB logo while performing the lookup.

In March 2001, CDDB, now owned by Gracenote, banned all unlicensed applications from accessing their database. New licenses for CDDB1 (the original version of CDDB) were no longer available, since Gracenote wanted to force programmers to switch to CDDB2 (a new version incompatible with CDDB1 and hence with freedb). The license change motivated the freedb project, which is intended to remain free.

freedb is used primarily by media players, cataloguers, audio taggers and CD ripper software. As of version 6 of the freedb protocol, freedb accepts and returns UTF-8 data.

...
Wikipedia