free cross-platform music creation software
Chip style MIDI synthetizer
Polyphonic MIDI sequencer
ZynAddSubFx and Yoshimi midi control
A graphical interface GUI for Fluidsynth Soundfont Player
Music notation editor
A GUI Frontend for Linux chiptune emulator
Very Powerfull Crossplatform Qt Based Music Note Editor[Still Planing]
To send OSC messages with a graphic tablet
A GPL software synthesizer for all.
Just an FX Processor...
Yamaha TG55 tone generator MIDI front panel