Although Duet Display is not the first app to allow your iOS device to act as an extra display for your Mac (Shape's $10 iDisplay comes to mind), it's the first app to have done screen extending right.
Built by ex-Apple engineers who worked at the company for three years on the iPad and iMac, the software delivers a Retina display at a smooth sixty frames per second with no lag whatsoever.
Featuring touch control, Duet Display makes interactions with your Mac fun and smooth while taking advantage of the fact that an additional display increases productivity by giving you up to 48 percent more pixels to work with.