Jeff Han's Multi-Touch

This is my absolute favourite and is a popular video on YouTube.

Jeff Han's multi-touch - marketed by his company, Perceptive Pixel is ...
now what is it actually?

It's not an interface as he states that there isn't one because you are interacting directly - so is it an input or output device? Both really, I suppose. This is as 'direct manipulation' as it gets. It is totally scalable so you can have an interactive wall if you like and as many users as required - multi-touch means multi-user.

If you've never seen this in action, watch the video as you're in for a treat...