Doubles
Join a pairing call from Windows, Linux, ChromeOS or any Mac. You can watch, talk, point, draw, ask to take control and drive once the person sharing allows it, and share your own screen for others to watch.
This page isn't using https, so your microphone, camera and screen sharing are off. You can still watch, point, draw and take control. Ask the host for the https address.
On a Mac, the Doubles app can also be controlled, shares sharper (up to native resolution), and transcribes and records calls.