From the Reactable homepage: “The reactable is a collaborative electronic music instrument with a tabletop tangible multi-touch interface. Several simultaneous performers share complete control over the instrument by moving and rotating physical objects on a luminous round table surface. By moving and relating these objects, representing components of a classic modular synthesizer, users can create complex and dynamic sonic topologies, with generators, filters and modulators, in a kind of tangible modular synthesizer or graspable flow-controlled programming language.”
Reactable fuses ARToolkit like marker tracking with an audio synthesis module and an impressive visual feedback system. The marker tracking code is avaliable in the software section of their main website. Bjork uses this system during her live performances, most recently at the 2007 Glastonbury festival.
Check out some of the videos: Reactable basic demo #1, Reactable basic demo #2 and Reactable improvisation demo.
More videos avaliable on the Reactable homepage.