The nice people that made the reactable have released the engine behind the table under the GPL.

As a multitouch interface used by musical artists including the legendary Bob Moog and Björk on her Volta world tour (Live Videos on Youtube Later with Jools Holland and at the Coachella Festival 2007 ) this user input technique gives real hands on approach to computer interaction.

The multitouch experience is genuinely play like and most importantly, very user friendly.

Behind the scenes computer vision blob detection algorithms facilitate multiple object detection and tracking, controlled through the 'Tron' like interface of the music table.

Away from the music table the engine itself recognises amoeba type objects called fiducial markers and can track their x+y coords, as well as the rotation around the z axis.

The reacTIVision app spews out this information using the TUIO protocol, which means that anything that uses OpenSound control can tap into it. It can also send messages as MIDI.

And they've got example code for use in most of the major 'software you use to display nice stuff', including Flash and Quartz Composer.

So far Cogapp experiments with multitouch systems like reactable have proved a fun way to interact with technology, adapting the complexity behind the scenes to produce an engaging and intuitive natural user interface.