GoatTracker - This is a crossplatform C64 music editor.
ZynAddSubFX - ZynAddSubFX is an open source software synthesizer for Linux, Mac OS X and Microsoft Windows.
OnlineSequencer.net - OnlineSequencer.net is an online music sequencer that allows users to create beats and music tracks.
Qsynth - Qsynth is a simple Qt4 application wrapper for the ...
Jummbox - A modified Beepbox that have more stuff then Beepbox. It can be used just like Beepbox. The features of Jummbox is the same of Beepbox's features, but Jummbox have more stuff to offer.
Surge XT - Open-source subtractive-hybrid synthesizer formerly sold commercially as Vember Audio Surge.