SynergyNet is a free and open-source framework that allows you to create platform independent multi-touch software.
Note that an external vision system (such as CCV) should be provided in order to work properly.
Also, SynergyNet uses several Java libraries, such as JME for creating networked applications that can also employ multi-touch inputs.
Detailed instructions on how to install and use the SynergyNet utility on your Mac are available HERE.
SynergyNet is cross-platform and it works on Mac OS X, Windows and Linux.