I personally switched from NextCloud to Syncthing.

Syncthing:

• is easier for me to maintain,
• allows for the "server" to be behind NAT,
• lets me have multiple "servers" at the same time (eg. something at home and a VPS)
• lets me have certain "servers" set as untrusted, so all data on them is encrypted, while others can have it unencrypted for easier access I put "server" in quotes, as Syncthing doesn't really have a server, all clients are equal peers.

On the other hand, NextCloud:

• gives me a way to share files by link with others,
• lets me browse files via a web interface,
• mobile app lets me access files as I need them instead of having to synchronize everything.

I wonder how it compares with Ergo IRC Server. Seems to take the more minimalistic approach.

It uses systemd services. My understanding is that it aims to have the applications installed in the most straightforward way possible - avoiding containers where possible.

Looks like YunoHost, but hearing about the licensing issues, I'll stick with YunoHost.

I did! Don't expect too much stability out of it, but I was surprised to say that the latest version worked pretty stable and nicely for me. I can definitely recommend it.

It's mandated by the EU: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:52021XC1229(06) (see point 6a).

Matrix works, but it's way harder and more expensive to selfhost than for example XMPP, which can be hosted even on cheapest VPS or first RPi. I would definitely take the cost and "how hard is it to maintain in the long run" into consideration.

Mattermost also works and is pretty easy to selfhost, but it doesn't have federation.

Another option is always an email with delta.chat - I don't think it offers voice calling, but email is one of the most basic services one can host, and many automated solutions to help with that exist.