I first read about this a couple of years back. They have come a long
way. Looks really fun to use now:
http://mtg.upf.edu/reactable/
The reactable, is a state-of-the-art multi-user electro-acoustic music
instrument with a tabletop tangible user interface. Several simultaneous
performers share complete control over the instrument by moving physical
artefacts on the table surface and constructing different audio
topologies in a kind of tangible modular synthesizer or graspable
flow-controlled programming language.
--
Patrick Shirkey - Boost Hardware Ltd.
Http://www.boosthardware.com
Http://lau.linuxaudio.org - The Linux Audio Users guide
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"Anything your mind can see you can manifest physically, then it will
become reality" - Macka B