SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker). It is a tool for those people who like to compose music wherever they are, whenever they wish. On any device.
MilkyTracker is an open source, multi-platform music application for creating .MOD and .XM module files. It attempts to recreate the module replay and user experience of the popular DOS program Fasttracker II, with special playback modes available for improved Amiga ProTracker...
Psycle is a Music tracker (like FastTracker 2 or Impulse Tracker) combined with plugin modularity. It supports its own plugin API, the VST2 plugin standard, and a tracker style sampler playback.
BlokDust is a web-based music making app. By joining blocks together, you can build synthesizers, put effects on your voice, remix & manipulate samples and arrange self-playing musical environments.
Buzz is the first ever "easy to use" free modular software based synthesizer. What this means is that the entire system is based on objects, which may be routed in a modular fashion, giving you the freedom to be as creative as you want.