Note: this post is from 2007, outbound links may be broken.
Music Animation Machine MIDI Player
The Music Animation Machine MIDI Player is a freeware application for Windows PC.
With this program you can listen to your own MIDI files (or play live) while viewing visualizations like these:
harmonic compass + pitch bars, circle of fifths color wheel and part motion visualizations
The Music Animation Machine display is a score without any measures or clefs, in which information about the music’s structure is conveyed with bars of color representing the notes. These bars scroll across the screen as the music plays. Their position on the screen tells you their pitch and their timing in relation to each other. Different colors denote different instruments or voices, thematic material, or tonality. And each note lights up at the exact moment it sounds, so you can’t lose your place.
Check these videos to see how MAM works.
Link via Waxy.org