Touchless

Touchless enables touch without touching by using a webcam to track color based markers.

Touchless includes two parts:

• Touchless Demo is an open source application that anyone with a webcam can use to experience multi-touch, no geekiness required. There are 4 fun demos: Snake - where you control a snake with a marker, Defender - up to 4 player version of a pong-like game, Map - where you can rotate, zoom, and move a map using 2 markers, and Draw - the marker is used to guess what.... draw!
• Touchless SDK is an open source SDK that enables developers to create multi-touch based applications using a webcam for input, geekiness recommended.

This project is an Office Labs community project. So you can also download it's SDK, try the application or watch demo video from the source.