This is an amazingly cool project that’s relatively easy to build with a high geek cred payoff: a “Time Fountain,” a fountain that appears to suspend the drops falling from it. Basically, it’s a little desktop pump-powered fountain with Fluorescein liquid (a fluorescent dye) in the water and UV LEDs controlled by a PIC16F628. By timing the strobe of the LEDs to the dye flow, you can appear to suspend the drops, make them go backwards, even manipulate them. Very cool.
You definitely want to watch the video. The project posting is followed by a nice long thread about the Time Fountain, where to find the parts, programming the PIC, and more.