Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
Voicemod - What are the voice changers? How do these work? Are these illegal? What is a soundboard? Find all the answers here. Voicemod - The Best FREE Voice Changer
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Clownfish Voice Changer - Clownfish Voice Changer is multiple voice changing software for various chatting and gaming platforms.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
JN Soundboard - An open-source hotkey soundboard program