Captain Chords - Write chord progressions in your favorite DAW
Tonelib JAM - Create, edit, print and listen to tablature and guitar sheet music
Odesi - ODESI is a music sketchpad that exports your projects to Audio and MIDI.
Chordsheet Maker - Create chord sheets or lead sheets quick and easily from your iPad. Add rhythms, endings, segno, codas and all what's necessary for your musicians to know what's your music about. Transcription made easy!
Cthulhu - VST MIDI-FX plugin for harmonic inspiration
Aria Maestosa - Aria Maestosa is an open-source (GPL) midi tracker/editor.