Screens often sit around doing nothing, the lazy black rectangles. Luna Display ($69.99) can bring one to life, transforming it into a screen for your Mac. The hardware component is a tiny dongle you connect to the host Mac, either via USB-C or Mini DisplayPort. The receiving device then becomes a display for that Mac, updating over Wi-Fi. That probably sounds a lot like Sidecar, built into macOS Catalina. But Luna Display goes further than Apple’s solution, which merely lets you use an iPad as a second screen. With Luna Display, an iPad can be used in a headless mode, with a Mac mini or Mac Pro. And the new Mac-to-Mac mode gives you a reason to power up any creaky old iMac or Apple notebook running Mac OS X Mountain Lion or later, using its display to usefully extend your desktop.
Tablets & computers