Hard to say, I don't really use discord so I think of it as voice chat as a service, and for pure voice chat it is hard to do better than mumble. However from the way people talk about discord, it is also a text chat screen sharing file server. and it is hard to find one product that does all that well.
For video, both video chat and screen sharing I have had a lot of success with Galene, it
offers text chat and file sharing, but they are sort of anemic and bare bones, which could be good or bad based on the needs of your users. https://galene.org/
What I usually do is start with a fossil server, this is trivial and gives you files, a wiki and a forum (none of them super good but like I said trivial to set up) then if I want voice, mumble is my normal route, but galene is growing on me more and more, the web interface makes buy in from the end users trivial and despite it being nice you almost never need the cool room stuff you can do with mumble.
But I am a sys-admin, I like running servers, hell, I find I enjoy running the servers more than I like playing the games. Plus, statistically, I have zero-friends, it is fine to say a server is great when only one other person has used it. That is to say, my results may not be typical.
For video, both video chat and screen sharing I have had a lot of success with Galene, it offers text chat and file sharing, but they are sort of anemic and bare bones, which could be good or bad based on the needs of your users. https://galene.org/
What I usually do is start with a fossil server, this is trivial and gives you files, a wiki and a forum (none of them super good but like I said trivial to set up) then if I want voice, mumble is my normal route, but galene is growing on me more and more, the web interface makes buy in from the end users trivial and despite it being nice you almost never need the cool room stuff you can do with mumble.
But I am a sys-admin, I like running servers, hell, I find I enjoy running the servers more than I like playing the games. Plus, statistically, I have zero-friends, it is fine to say a server is great when only one other person has used it. That is to say, my results may not be typical.