The Mutopia Project
The Mutopia Project offers sheet music based on editions in the public domain. All sheet music is written in LilyPond by volunteers and the entire archive is openly available for download. If you are new to the project please visit MutopiaProject.org and browse the sheet music.
This GITHUB repository is made available to promote this volunteer effort. There is a wiki available if you are interested in contributing using GITHUB. Please see the main website contribution page for information on how to submit by email if you are not comfortable with GITHUB.