I'm helping students and people with disability to navigate their devices and learn how to do things on their computer.

Sometimes I do this remotely, and I'm looking for software that would allow them to share their screen to me. And me to annotate on their screen (visible to them) or at least show my cursor so I can point at things.

I know this used to be possible with slack. But I would like to find an open-source and affordable alternative.

Anybody have some experience with this?