It’s a real shame that essentially all modern communication other than email runs over proprietary protocols.

We use a lot of sip with all manner of endpoints

Sure, in a way SIP is bigger than ever with NGNs, and there’s SIP use beyond that too, but actual interoperable SIP (as in, I can dial sip:[email protected]) is effectively not a thing anymore.

I don’t deal with corporate telephony but our sip accounts on the broadcast side have all manner of endpoints, including software and hardware from many different manufacturers. We land them on a pair of paired oracle sbcs which somehow (I’m not close to the details on this part) shares account detail and sessions between the two geographically resilient locations.

You just need the dns, account and password.

I do believe that vendor-interoperable SIP exists today, but I also know that I can't call >99.9..9% of the people in the world via SIP, and 100% of the ones I practically do call.

This is a very different story from e.g. email – even though most people I communicate with use either Gmail or some hosted Outlook service, I don't have to on my side (with some limitations around deliverability etc. lately).

I also miss proper chat systems over proprietary ones. Slack offers very little utility over IRC.

Slack has a button you can use to add custom emojis. Mic drop.

IRC the protocol is pretty good still, specifically with the ircv3 additions. It's the clients that are janky still. I still remember when Slack ran a free IRC bridge for their chats...