Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
Fission - Edit audio in minutes, not hours.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Audio Cleaning Lab - Looking to clean up your song recordings? Download SOUND FORGE Audio Cleaning Lab, the professional solution for cleaning & restoration with advanced ProAudio technology.
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.
LMMS - Make music with a free, cross-platform tool