Use your iPhone as a second screen for your Mac

Once connected, tap “⋯” → “Choose Display” → “Second Display”. Within about a second your Mac gains a new display named “TouchNow”, and that new desktop is what your iPhone shows. If the option isn’t there, update TouchNow Host on the Mac to the latest version.

Drag windows onto it or run an app full screen there; the menu bar and Dock behave just as they do on a real external display. Control it from the iPhone with the trackpad or by tapping directly, or simply move your Mac’s own mouse over to it. To change which side it sits on, drag it around in “System Settings” → “Displays” on the Mac.

The size is set from your iPhone’s screen at the moment you tap “Second Display”, at Retina sharpness. To change it, switch back to your original display in “Choose Display”, then turn it on again. Switching back or disconnecting removes the extra display, and macOS moves its windows back to the main screen.

The Mac’s built-in Sidecar only supports iPad. TouchNow lets an iPhone be the extended display too, and iPad works as well. No cables, no extra hardware.

If all you want in your hand is one window, such as a music app’s controls or a chat, “⋯” → “Choose App” streams that single window while the rest of your Mac screen carries on as normal.

No. On the same Wi-Fi it is free, like every other feature.