GDancer is a visualization plugin for XMMS which animates the lovable cartoon character Space Ghost to your favorite MP3s. You can also have other characters through themes.
Scivi is a visualization plugin for XMMS, the X Multimedia System. It
uses OpenGL for rendering and a C-style scripting language to define the
visualization types you want.
An FFmpeg and SoX based EBU R128 compliant loudness scanner for audio files.
An online interactive tutorial and free text assesments.