Ask HN: Can you suggest self-hosted chat/audio system with Android/iOS client

Apologies if this question was already asked, I could not find good answer here but maybe I was not using the right keywords.

I would love to host a system for my family (including my grandma who is not very technical) and friends that would let us communicate over messages and audio calls (if video calls would be possible then I would be in 7th heaven)

Can you share what you are using (if you have done something like that)?