Plane9!

MilkDrop is an open source, hardware-accelerated music visualization plugin for Winamp, which was originally developed by Ryan Geiss. It uses DirectX and intelligent beat detection to render iterated images which blend seamlessly. MilkDrop uses a complex system of interpolation to transition between presets gradually through time, creating a constantly changing visual experience.

Visualize your favorite tunes online for free with APEXvj, featuring some of the most advanced music visualizations in the world.

projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL. All projectM requires is a video card with 3D acceleration and your favorite music.

Kauna is a music visualizer. Kauna renders any sound reproduction in system. It can also capture audio from a microphone.

And what is Cthugha (pronounced "Kah-Thoo-Gah")? It's a free program available for PC's (running DOS, Windows, or Linux) and Macintosh's which takes sound input from a CD, stereo, or microphone and displays colorful animated graphics synced to the sound. Sort of like an oscilloscope, but on LSD.

VSXu Ultra Artiste lets you create stunning open GL based audio reactive visuals. Its unique modular interface gives you drag and drop functionality gives you access to dozens of modules that allow easy compositing of presets that can be played in VSXu player.

Morphyre is a 3D Music Visualizer and Screensaver for PC and Mac that runs as a Plugin in iTunes, Windows Media Player, Winamp, or on its own. It's also now available for Android devices.

G-Force features fast anti-aliased visuals, millions of possible effect combinations, savable and scriptable effects, and unparalleled expandability. G-Force is designed to entertain you on its own, but there are many ways it can be customized and extended.

R4 is a standalone OpenGL accelerated program (created by Gordon Williams of RabidHaMsTeR.Org) which aims to produce animated 3D graphics in real-time that twist and turn with the music. The WinAmp-based precursor to R4 (R2/Extreme) is now used in many nightclubs, at parties, and has been used at many massive events such as Glastonbury (by Psyrcus Wyrd), and the Ministry of Sound New Years event (at the Millennium Dome in London).

Visualisator 5000 is an awesome Music Visualisation App for your Android phone or tablet!Just start your favourite mp3 player, put it in the background, start the Visualisator 5000 and enjoy the trippy 2D and 3D graphics created by YOUR music!

Really Slick contains free 3D OpenGL screensavers. All of these savers are colorful and exhibit rich animation that never repeats. Some are based on classic screensaver themes, such as fireworks, swarms, and plasma. Others are more original and psychadelic, with geometric patterns based on principles of physics and mathematics. The screensavers are originally written for Windows, but the downloads page contains links to ports of other platforms such as Mac OS X and Linux.

Experience music in a new light! Get ready for an endless journey through a corridor of color and sound. Don't just listen to your music, follow it down the Rabbit Hole!