Your computers, from your phone.
Nothing is shared until the person at the computer clicks Allow, or you use the password set on that computer. While connected, a red bar at the top of their screen says so, with an End button.
On a phone: tap to click, hold to right-click, pinch to zoom. Switch between Move, Scroll and Drag at the bottom. The keyboard button opens your phone's keyboard.
Windows may say "Windows protected your PC" the first time, because ReachDesk is new: click More info, then Run anyway. On a Mac, open the zip and follow READ ME FIRST.
Add this page to your home screen (Share → Add to Home Screen) to open it like an app.