Mutopia Project

The Mutopia Project is a volunteer-run effort to create a library of free content sheet music, in a way similar to Project Gutenberg's library of public domain books. It started in 2000.

The music is reproduced from old scores that are in the public domain. New scores are digitally typeset with GNU LilyPond and distributed in the following formats:
 * PDF format in both letter and A4 paper sizes for printing,
 * MIDI for aural reproduction, and
 * LilyPond source code format.

, there are 2124 pieces of music available, over a third of which are for piano.