Multitrack audio editor
Featureful native Commodore 64 music tracker with MIDI/XM converter
An algorithmic music composition system
Free music notation & composition software
Become DJ and propose playlists to your friends
Buzztrax is a modular music composer for Linux
free cross-platform music creation software
Just Intonation Synthesizer For X Window
Very Powerfull Crossplatform Qt Based Music Note Editor[Still Planing]