Mumble for voice chat. (It already beats Discord in that department.) A server can be self-hosted, or rented for dirt cheap.
Matrix is getting better all the time, and although it won't replace all of Discord's features today, it is catching up. I already use it for text chat, and wouldn't be surprised if it could take over for video, screen share, etc. in the next year or so.
Tip for people wanting to try Matrix now: Consider disabling encryption on your Discord replacement rooms until Matrix 2.0 is fully released, to avoid occasional frustrating glitches. That won't be a loss coming from Discord, which doesn't have end-to-end encryption anyway.
Let's not forget an even bigger problem with Discord: It locks your communities, including contacts and years of content and discussions created by members, behind some corporation's ~~terms and conditions~~ whims. You (or your friends, or the "server" admin) can lose access to it all at any time, without warning. They can and have used this as leverage to extort personal info from people. A policy change, accident, or technical glitch can leave you out in the cold.
This alone is reason enough to avoid it.