Air Display is an easy way to get extra screen real estate from another computer, smartphone or tablet. Just install the app on one device, install its receiver program on another and you should be using a second screen in no time. The app doesn’t require any extra cables or connectors. Moving from screen to screen is fairly smooth. The program runs on Apple devices but can be used to expand your screen from Mac to Mac, iOS device and Android or from Windows to iOS device, Android or Mac. $9.99 for iOS devices or $19.99 for the Mac. The receiver program is a free download.