The mutopia project is a collection of public domain sheet music. You can help the project by entering music and submitting. Point your browser to the Mutopia webpage. If you know a little MetaFont you can contribute a glyphWriters. The documentation of LilyPond and related utilities needs a lot of work.
Hackers There are lots of possibilities of improving the program itself.
There are both small projects and big ones. Most of them are listed in the TODO file. A interesting and very big project is writing a GUI frontend to LilyPond. The Free Software Directory Volunteers are needed to help compile a directory of known free software . This task entails downloading free software packages, digging up information about these packages, and checking and verifying the licenses of the programs.