Are you interested in multi-touch gestures for multimedia tabletop applications, tangible or surface computing, and interaction design? Take a look at this video of Grafiti:
Alessandro De Nardi, a student in computer science at the University of Pisa, Italy, has worked on Grafiti during Google's Summer of Code and is still involved with the project. Alessandro, a member of the NUI-group, is also in the Music Technology Group of Barcelona's UPF University. Allesandro was supervised by by Martin Kaltenbrunner and Sergi Jorda, of the reactable project.
According to De Nardi's Google Code website:
"Grafiti is a C# framework built on top of the Tuio client that manages multi-touch interactions in table-top interfaces. The possible use of tangible objects is particularly contemplated. It is designed to support the use of third party modules for (specialized) gesture recognition algorithms. However a set of modules for the recognition of some basic gestures is included in this project.
The development is in the alpha state, going to beta soon.
The goals I've been aiming at are: generality, versatility, speed of execution, extensibility, ease of programming (integration) of external modules (simple APIs and protocols) and effective interface design with regards to HCI aspects." -Alessandro De Nardi
Demos in binary form are available for download for MacOSX and Windows on the Google Grafiti site. There is a Grafiti site on Sourceforge. Apparently the alpha version will work on all 32-bit MS Windows,, BSD platforms, and POSIX (linux).
(Note: This post was updated on 12/14/08 and includes corrections.)