VCV Rack - A cross-platform modular synthesizer.
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.
miRack - Eurorack-style modular synthesizer for iOS.
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
SynthEdit - Visual programming software to build your own synthesizer.
Cubasis - Cubasis is Steinberg’s streamlined, multitouch sequencer for the iPad.