Robin Good has great collections of free collaboration tools http://tools.robingood.com/content/home/387#search/latest/none/all/3685/all/1/1/latest/30/0 I saw there webroom.meet which looks on par with appear.in (I’m still using that frequently; it’s web recording requires a paid upgrading, but fantastic for informal meetings w/o no login)
I once used Jitsi meet- it’s an open source tool but cannot remember if its a thing one needs tech wizard skills to install on server https://jitsi.org/jitsi-meet/
I used Adobe Connect alot in my NMC days (pre 2011) and recently used it again, hardly changed. It also crashed on me twice while presenting, but might have been meet.
There’s all the business tools like GoToMeeting ($) and a few more https://www.hongkiat.com/blog/online-meeting-tools/
The thing harder to gauge is knowing the network infrastructure that hosts the thing, since Google is huge, I’m inclined to think they are more robust (assumption?). For smaller ones, like big blue button, appear.in the experience is a lot at the whim of all the internet connectivity problems in between, hard to truly assess for cross the board (and hence the reason to judge a tool by our good/bad experiences in it).