Wallpaper Engine - Wallpaper Engine enables you to use live wallpapers on your Windows desktop.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
ScreenPlay - Open-source and cross-platform Wallpaper, Widgets and AppDrawer app.
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
Lively Wallpaper - What is it? Lively is a Free and Open-Source Software (FOSS) for animated desktop wallpapers.
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.