Remember putting your eyes up to the end of Kaleidoscope and rotating it around to have a magical burst of colors dance in front of you? In case you do (or don't) try playing with this fancy virtual tool by zefrank. It's not quite the same as the real deal, but this way you get to build your own Kaleidoscope with nothing more than a black circle, basic geometric forms, and a rotating blue wedge. My final result was way cool, and I used all the pieces.
Warning: Don't stare at the rapidly moving colors too long. You may start to feel sleepy, very sleepy.