LilyPond

Screen dump: 
LilyPond screen dump

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 processes human-readable text files that can be edited in any text editor. These files contain all the information about the content of the score, which LilyPond compiles taking care of every detail to create a beautiful score. It also allows the user to change the layout of the score by adding human-readable layout information to the same text file.

There are a lot of tools available to facilitate the creation of scores with LilyPond, such as Frescobaldi, Denemo and extensions for Emacs and Vim.