Stave'n'Tabs - iOS and macOS notation and tablature editor with MIDI and MusicXML files support and chromatic...
wxWidgets - wxWidgets: Cross-Platform GUI Library
Tonelib JAM - Create, edit, print and listen to tablature and guitar sheet music
Electron - Build cross platform desktop apps with web technologies
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!
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.