SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
ZynAddSubFX - ZynAddSubFX is an open source software synthesizer for Linux, Mac OS X and Microsoft Windows.
FamiStudio - FamiStudio is very simple music editor for the Nintendo Entertainment System or Famicom. It is designed to be easier to use than FamiTracker, but its feature set is also much more limited.
Qsynth - Qsynth is a simple Qt4 application wrapper for the ...
MOTU Digital Performer - Get inspired, then refine your mix — all in a singular workflow.
Surge XT - Open-source subtractive-hybrid synthesizer formerly sold commercially as Vember Audio Surge.