Freedb

Also known as freedb.org

Freedb was a database of user-submitted compact disc track listings, where all the content was under the GNU General Public License. To look up CD information over the Internet, a client program calculated a hash function from the CD table of contents and used it as a disc ID to query the database. If the disc was in the database, the client was able to retrieve and display the artist, album title, track list and some additional information.