The Touchless SDK enables developers to create multi-touch based applications using a webcam for input. Touch without touching. Touchless is released free and open-source to the world under the Microsoft Public License (Ms-PL) on CodePlex.
The Touchless SDK is a set of .Net components that can be used to simulate the gestural interfaces of devices like the iPhone in thin air — using nothing fancier than an ordinary USB Webcam. Neil McAllister in his article gives a detailed explanation and also discuss ARToolkit is a cross-platform library that can achieve many of the same things as the Touchless SDK. ARToolKit is a software library for building Augmented Reality (AR) applications. These are applications that involve the overlay of virtual imagery on the real world.
The immediate future seems to become mouseless. Gestural interfaces will be the next cool thing.