From the YouTube page:
"The reactable, is a multi-user electronic music instrument with a tabletop tangible user interface. Several simultaneous performers share complete control over the instrument by moving physical objects on a luminous 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.

This instrument is being developed by a team of digital luthiers (Sergi Jordà , Martin Kaltenbrunner, Günter Geiger and Marcos Alonso), at the Music Technology Group within the Universitat Pompeu Fabra in Barcelona, Spain."

There's already another video on here about this table. This one explains what the different objects do and how they are used.

More info here: http://mtg.upf.edu/reactable