Audio Tag Editor
GUI to work with abc notation
View and edit DICOM tags (Windows & Mac & Linux)
An Audio/MIDI multi-track sequencer
Graphical editor software for many Boss and Roland effect & synth unit
Qt XG Editor
it's a video player, also works for music and pictures
Sound Editor for KDE
Music score editor
Free yourself
Playlist Editor
free cross-platform music creation software
Music notation editor
Very Powerfull Crossplatform Qt Based Music Note Editor[Still Planing]
A GUI foundation for creating U/I based content
Music player with a customizable widget