What is your actual use case?
Since you mentioned “playing games with” and you are willing to try “Mumble”, I guess you are primarily interested in live voice chat with groups?
And you have other means to contact your “play mates” via chat?
For chat and community, I really like what the Techlore Team has done with “discuss.techlore.tech”.
For Group Voice Chat, I’d say Murmur (the Mumble Server) would be the best solution. I played with it a few years back but just within a local network.
Here are other services that came up and I have personal experience with:
Matrix (Synapse) - Great for Organisations to have their own MS Teams / Slack / WahtsApp like infrastructure. But presumably not great as a discord replacement.
XMPP (Prosody) - A lot of Work to setup, if you want all the features to work. Android and Linux Clients are great, others are not and the client selection causes me to switch (mostly) to Matrix instead.
Nextcloud Talk - Has great integration with Nextcloud and is only a good Option, wehen you want to build your own Nexcloud based eco system. To use it properly, you have to install the High Performance Backend, which was to much work for me till now.
Mumble (Murmur) - I can’t barely remember but don’t think it was that hard to setup.
RocketChat - I gave up on that one after screwing up my attempt of a working server setup.
Jami - This is client only. It wasn’t very reliable and the Apps crashed a lot.
Signal - Works great, requires a phone number, but still my favorite communication tool for chat, audio- and video-calls.
Jitsi Meet / Big Blue Button - For Video and Audio conferencing. I used them and really want to setup my own server soon.
That’s it - at least assuming you want primarily a real time audio conferencing solution for playing games together. - I hope this was helpful to you.