scoring and typesetting

LenMus Phonascus is a program for studying music theory that allows you to focus on specific skills and exercises, on both theory and aural training.

TuxGuitar is a free guitar tabulature editor and player, similar to the proprietary Guitar Pro. It can open GuitarPro, PowerTab and TablEdit files.

Denemo is a music notation program that lets you rapidly enter notation which it typesets using the LilyPond music engraver. Music can be typed in at the PC-Keyboard, or played in via MIDI controller, or input acoustically into a microphone.

Frescobaldi is a text editor designed to facilitate the creation of LilyPond music scores. Some of its features are:

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.

MuseScore is a powerful music notation editor for the creation, editing and printing of various types of musical scores.

Some features include WYSIWYG creation and editing, support for unlimited staves, unlimited score length, up to four independent voices per staff, percussion notation, a plug-in architecture, and excellent looking notation.

Full list of features

There is also a community site for sharing sheet music made with MuseScore -

MuseScore.com