For chat: IRC, Stoat, Fluxer, Root, Zulip, Matrix, Slack, Teams, Guilded.

For voice/video: Mumble, Teamspeak, Jitsi Meet, also several of the above.

Perfect 1:1 drop in hassle free replacement with the exact same feature set? No, there isn’t.

Viable alternatives that aren’t too bad to learn? There are many.

I quit drinking. I wasn’t an alcoholic or anything, but I was drinking regularly. Quitting has saved money on my grocery bill, made going out cheaper, made me healthier, and enabled me to remember every fun night with my friends with perfect clarity.