LilyPond

LilyPond is a music engraving program, devoted to producing the highest-quality sheet music possible. It brings the aesthetics of traditionally engraved music to computer printouts. LilyPond is free software and part of the GNU Project.

LilyPond came about when two musicians wanted to go beyond the soulless look of computer-printed sheet music. Musicians prefer reading beautiful music, so why couldn't programmers write software to produce elegant printed parts?

The result is a program that creates beautiful sheet music following the best traditions of classical music engraving. It takes care of the details of layout programmatically, allowing composers, transcribers and publishers to focus on the music instead of improving their software's default output. Performers will get parts that let them concentrate on playing music instead of reading it.

LilyPond allows musicians to produce elegant sheet music that is easy to read. Its developer community has spent thousands of hours developing powerful music engraving software that results in beautifully engraved music. All of LilyPond's style settings, font designs and algorithms have been inspired by the finest hand-engraved music. LilyPond output has the same strong, balanced and elegant look as the best-engraved classical scores.

This is further explained in this Essay.