Just saw this
https://opensource.com/article/20/5/free-software-communication
List of open source remote communication.
As you know I'm going to try a Jitsi meeting tomorrow. I'm going to use the
meet.jit.si server but it is possible too run your own Jitsi meet server.
Right now it seems that Zoom is the most popular one. I looked at it myself and was taken aback at having to download and run something. But it turns out you can run zoom from the browser.
Go to a zoom link. You get a pop up to run something. Cancel that and find "click here if doesn't open". Cancel the pop up again. Now near the bottom is "run in browser".
Thomas