Laurence Muller, M.Sc. is a scientific programmer at the Universiteit van Amsterdam who develops scientific software for multi-touch devices. His blog, Multigesture.Net, provides good information regarding multi-touch and gesture interaction hardware and software applications.
Laurence links to the DYI tabletop computing bootcamp that was held at
IEEE Tabletops and Interactive Surfaces 2008. From there, you can find a linked list of the organizers of the events, and additional information.
Picture below is from MTC Multi-touch Console:
Here is a link to the group's libavg wiki that includes open-source code and "how-to" instructions.
If you are interested in multi-touch and multi-gesture computing from an academic point of view, Florian Echtler, of the Technische Universitat Munchen has a series of publications listed on his website. Here is the abstract of one of his papers. He is on the right track. I especially like the fact that he's thought about widget layers. (I have, too, but they are only sketches in my idea book.)
TICH: Tangible Interactive Surfaces for Collaboration between Humans (Sourceforge website, with links to libtisch.
F. Echtler, G. Klinker
A Multitouch Software Architecture
NordiCHI 2008: Using Bridges, 18-22 October, Lund, Sweden. (bib)
"In recent years, a large amount of software for multitouch interfaces with various degrees of similarity has been written. In order to improve interoperability, we aim to identify the common traits of these systems and present a layered software architecture which abstracts these similarities by defining common interfaces between successive layers. This provides developers with a unified view of the various types of multitouch hardware. Moreover, the layered architecture allows easy integration of existing software, as several alternative implementations for each layer can co-exist. Finally, we present our implementation of this architecture, consisting of hardware abstraction, calibration, event interpretation and widget layers."