You're using multi-touch when you send SMS, receive your phone call, and so forth. If you have a Mac, then you probably control your Mac with multi-touch.
Now we are familiar with the idea of using our fingers (not a finger) to control cute gadgets. If using several fingers is that convenient, why don't you use two hands? Of course, this question is pursued by R. Clayton who proposed 10/GUI.
There are another cool application using two hands. Roger Linn has showed a prototype musical instrument called LinnStrument. Although the video does not show two handed interaction, a drawing in the LinnStrument preview page definitely shows its ability of two-handed interaction.
Great GUI and cool application exit now. Then, the next step is actual implementation. TBoard is an attempt to provide an acceptable hardware platform for the two great ideas. Enjoy it!