Sometimes it would be really handy if you could just take the iPad that sits next to your computer and make it a second Mac screen. Thanks to some ex-Apple engineers, you can. Duet works on any Mac running 10.9 (or other computer running Windows 7) or higher, by installing a free app to enable your machine to connect to your iOS device. Then take an iOS device running iOS 7 or higher, and install the Duet Display app. Here's the catch: Buying the iOS app will set you back US$15.99 but it is universal so you only have to buy it once. If you already connect your iPhone or iPad to your laptop for charging or syncing, then Duet gives you a place to put your inbox, or your palettes, or whatever else doesn't quite fit on the laptop screen you have. Paired with a nice desktop stand or a Mountie, you can put that extra screen to good use (when it isn't streaming Netflix).