Basically, the reacTable is a flat surface that makes sounds and music by dropping different modules onto it, and positoning them so that get the sound you want.  Modules range from tone generators, to strobes, to noise gates, etc. etc.  It’s like a musical flowchart…
     From its designers at Pompeu Fabra University in Barcelona:

The reactable hardware is based on a translucent round table. A video camera situated beneath, continuously analyzes the table surface, tracking the nature, position and orientation of the objects that are distributed on its surface, representing the components of a classic modular synthesizer. These objects are passive without any sensors or actuators, users interact by moving them, changing their position, their orientation or their faces (in the case of volumetric objects). These actions directly control the topological structure and parameters of the sound synthesizer. A projector, also from underneath the table, draws dynamic animations on its surface, providing a visual feedback of the state, the activity and the main characteristics of the sounds produced by the audio synthesizer.

     Put simply:  I WANT ONE!

     In case you’re not getting it, I’m gonna post all three demo videos for this thing.  This first is Basic Demo #1.

     Does that deserve a, “Whoah!” or what?  This is cool stuff!  So we go on to Basic Demo #2:

     Starting to understand it?  Then you’ve gotta check out the Improvisation Demo:

     The fun part is, it’s components are not exactly “cutting edge.”  But the very idea of putting something together in this fashion is leaps and bounds ahead.  Serious kudos are due its creators!

     The “Cool” Factor doesn’t stop there.  This puppy even runs on Open Source software!

     Be certain to check out their website…

Tip: Anton, over at LR2