Frescobaldi is a LilyPond sheet music text editor for KDE4. It aims to be
powerful, yet lightweight and easy to use.

Mandatory for typesetting but not for compile: lilypond.

Optional tools: Not required for compilation. You can use rumor to insert
notes via midi (ex. keyboard) and timidity for midi playback. You need to
configure both timidity and some other midi playback program like
audacious.