Mumble was… fine. My friends actually moved to Discord from Mumble for our MMO stuff but that was primarily because it was easier to invite randos to the chat. That quality makes it almost impossible to break away from atm.
I recall the latency being only a little worse than Discord, but I think that’s because a friend set up the server at his work as a side thing (he also hosted Minecraft and Terraria). It’s not too complex to setup, but your quality will depend a lot on the computer and network you’re running. At least, it did for us, back in the day.
We’ve thought about alternatives to Discord. Old names were Ventrilo and TeamSpeak but they’re just not very modern. Plus, now almost every chat app has voice, too. Just, for features, it’s hard to beat Discord at this… though I’m willing to read the other comments to get for ideas, too. Lol
I teach, so trying to adjust old ppts for lecture got a little weird because it turned the bulletpoints into mailboxes, and equation formulas are done completely differently so libre just makes them uneditable (a picture?).
When things got wonky in lecture though I managed just fine. My students are much worse, they open shit in non-MS apps all the time (.notes for takehome exams, or like, keynote, whatever) and fuck up formatting all the time, often without even realizing it. (I do provide PDF alternatives at least). Explaining I use libre really easy in that case, lol.