ZynAddSubFx and Yoshimi midi control
GTK+ GM (General MIDI) Monitor for GM GM2 XG and GS events
Cross-platform C++ library to handle music from code
A free karaoke player for Linux and BSD
Raw MIDI application set
Interface specification to divide UI from DAW engine
MIDI multi track song writing in an ASCII editor!
Very Powerfull Crossplatform Qt Based Music Note Editor[Still Planing]
To send OSC messages with a graphic tablet
MIDI/Sysex editor for Waldorf Microwave II/XT/XTk