These balls are cool and useless -- my definition of art and fun. They are large rubber balloons with colored lights in them which change color when punched. Unleashed into a crowd, they hop along blinking and reacting to the crowd. They are primitive examples of the future of fun: audience participation and the merging of the tangible and informatics.
Here is a description from the maker's website, Tangible Interaction Design:
ZYGOTE is a lightweight inflated ball, illuminated from within, that responds to pressure applied to its surface. Interacting with the ball is simple: punch it, bounce it, squeeze it, or tap it and the ball's internal LEDs react instantaneously. Dozens of balls released to an energetic audience at a major music concert, transform the environment into a multi-sensorial, interactive playground, actively engaging the crowd in a shared experience. Each ball also can act as both an input and an output device by being networked to a central computer. This allows for more complex interaction, as the crowd can modify the graphics on a screen, make the balls light up in unison, or even affect the music.
Video that explains its mechanics and shows it in action.