If you remember using teamspeak or ventrillo… Their is a FOSS alternative called mumble that works similarly. Its essentially the closest to what you’re asking that has both VOIP and other features. Some communities especially mmorpg clans and gaming clans still use it. Idk how popular it is in general though. Discord is supported by huge donations which is why they’ve been able to dominate, but teamspeak/mumble still exist and essentially are the same thing but less modern.

https://www.mumble.info/

IRC and Matrix are both IM systems but are alternatives to discord if that’s all the functionality you seek. Matrix is also in the fediverse.