Tom says that when using Zoom, he runs into problems. Leo says that's because everyone is using the network, from education to working from home, and as such, it can get overloaded. Leo recommends Jitsi. It's free and open source. And he can run his own server for calls, as well. He can find others in this article at Computer World. But chances are, he is going to end up back at Zoom. It's largely ubiquitous.