Riveropolis is a little like a very intricate game of Pooh Sticks. It’s been a standby at Maker Faire for years now, and creator Gregory Gavin runs workshops and brings it to summer camps and even sells completed rivers. A river of molded fiberglass flows, alternately lazy and cascading, carries float boats built by kids out of corks, wood, and rubber bands.

It gives kids a chance to think about the process of design, says Gavin, without putting parameters on their success. It’s really kind of a free for all; kids circle the build tables and the river, testing and rebuilding their boats with little direction besides their own creativity.