The fact that this topic appears right now is quite the timing.
Yesterday night I dreamt about what the perfect such app would be (don’t judge me). I’m drafting a mock-up right now, as I might actually make it a project (I’ll probably make a post about it when this is all ready, although I don’t think this website is appropriate to self-advertise on).
As it turns out, there seems to be quite a few good alternatives to Discord. I don’t know Rocket.chat and it seems rather solid. If anyone has some inputs to give on what this (or these) apps are lacking, I’d be very happy.