ZynAddSubFX - ZynAddSubFX is an open source software synthesizer for Linux, Mac OS X and Microsoft Windows.
VCV Rack - A cross-platform modular synthesizer.
Qsynth - Qsynth is a simple Qt4 application wrapper for the ...
Pure Data - Pd (aka Pure Data) is a real-time graphical programming environment for audio, video, and graphical...
Surge XT - Open-source subtractive-hybrid synthesizer formerly sold commercially as Vember Audio Surge.
miRack - Eurorack-style modular synthesizer for iOS.