LilyPond is a music typesetter. It produces beautiful sheet music using a
high level description file as input. LilyPond is part of the GNU project.

LilyPond is split into two packages. The package "lilypond" provides the
core package, containing the utilities for converting the music source
(.ly) files into printable output. The package "lilypond-doc"
provides the full documentation, example .ly files for various features and
the Mutopia project files (musical equivalent of the Gutenberg project - see
http://www.mutopiaproject.org for details).

If you are new to lilypond, you will almost certainly want to install the
"lilypond-doc" package and take a look at tutorials under
/usr/share/doc/lilypond-doc.