Want to turn your iPad into a second display for your Mac? This is probably the best app for it.
Built by ex-Apple engineers, Duet lets you to connect your device to your Mac and use extra screen estate as desktop space. Depending on your device, the app is billed to improve your productivity up to 48% by allowing you to see and do more at the same time.
Connect your iPad to your Mac using the Lightning or 30-pin cable, launch the app, and enjoy your Mac desktop being extended between the computer and tablet. Apart from simplicity and hassle-free configuration, Duet comes with state-of-art technology that basically removes any lag when transferring the picture. In other words, the app works as good as an external monitor, but costs just a fraction of its price.