If you've every wanted to get into multi-touch programming, Community Core Vision (CCV) by the NUI Group is a great way to get started. It's an open source, cross-platform solution for computer vision that supports several multi-touch lighting techniques (FTIR, DI, DSI, and LLP).

It's very easy to get started using CCV and build a simple Front DI multi-touch device for prototyping. All you need is a cardboard box, picture frame and PS3 Eye Camera. Below is the video tutorial I used that explains how to build your own.

Once you have your hardware set up you can download CCV and start playing with the different Flash Example Clients available.