There is BigBlueButton. It’s more focused in educational usecases (online classes and the like) but it works just fine for everything else. You need to host it yourself, but there are hosted instances out there. I for example use senfcall.
But I think we are talking about different things here. What Chanuk was talking about (I think) is a ms-teams or slack alternative, not a zoom or oracle WebEx alternative. Basically Discord but for business. Sidenote: there is a open source Discord clone called revolt
He’ll, even an Intel based thin client would probably be enough. You can get them on eBay for like 30 bucks, which is about as much as a pi costs. You’ll probably have to replace the ssd though. That’ll set you back an additional 30 bucks.