CDDB

CDDB is a database for software applications to look up CD (compact disc)
information over the Internet. This is done by a client which calulates a
(nearly) unique disc ID and then queries the database. As a result, the
client displays the artist, CD-title, tracklist and some additional info.

CDDB is used primarily by media player and CD ripper software.

The initial CDDB license was GNU General Public License, and many people who
submitted CD information without charging anybody and thinking their help
would remain free. However the license was later changed and some
programmers complained that the new licence included certain terms that
threatened them in a way they couldn't accept: If you want to access CDDB,
you are not allowed to access any other CDDB-like database (such as FreeDB)
and - while accessing the database - the programmer has to ensure, that a
CDDB-logo is displayed.

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 not available anymore, as they wanted to
force programmers to switch to CDDB2 (a new version incompatible with CDDB1
and hence with FreeDB).

The licence change motivated a new project, FreeDB, which is intended to
remain free.

An alternative project that aims to enhance CDDB beyond a mere database of
CDs is called MusicBrainz. This site also contains more information on CDDB
and some database statistics of CDDB and FreeDB.