SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
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.
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
MOTU Digital Performer - Get inspired, then refine your mix — all in a singular workflow.
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.