Commands:
Page up: fast acceleration
Page down: fast deceleration
Up: slow acceleration
down: slow deceleration
F2: Show/Hide controls
Esc: Quit
S: Stroboscope
C: Rainbow colors
L: Light
D: Dark
F: Fade colors (on|off)
Space: Pause

If the applet doesn't work, install the latest version of Java available here.
Discotheek runs on Windows, Mac OS X and Linux.