Do you like interactive art? Imagine a bunch of little lights on a table, each about the size of a chess piece, each independent of the others. Arrange them any way you want. Each light continually and slowly changes colors on its own — but when you wave your hand over them, they create waves of colors that follow your hand. Trippy!
To go deeper, a 6-pin ICSP interface lets you use an AVR programmer or Arduino to reprogram each light’s behavior. To sense proximity, the lights use an infrared LED and IR detector. This is another awesome and affordable kit from Mitch Altman, the creator of the TV-B-Gone and the Brain Machine.