A joint project between the Shape Lab at Stanford University and the Aviz team at Inria (France) Zooids is an open-source open-hardware platform for developing tabletop Swarm User Interfaces.
The platform consists of a collection of custom-designed wheeled micro robots, a radio base-station, a highspeed DLP structured light projector for optical tracking, and a software framework for application development and control.
See the user interaction scenarios using the Zooids in the video below.
h/t @Bruces
