https://matrix.org fits the bill.

Ah, thanks! I came across that a while ago but had forgotten about it. It seems to have come along quite a ways.

Yes, their web & mobile client https://riot.im is very polished now. They are also rolling e2e crypto.

It may be a little over engineered for what I want it for, but it does work! I started up the reference server in a docker container and wrote a quick bot using the provided python-sdk and can interact with it using the client on my phone.

The main downside(from my perspective) is that it's a lot of moving parts, and I think I'd be more happy with just irc over tls since I at least know how that works :-)

It's mostly a question of mobile support: IRC (over TLS or otherwise) requires a continuous connection, where matrix and signal are designed to support polling a push notification endpoint.

Out of curiosity: what makes you say Matrix is over-engineered?

Oh.. maybe not over-engineered, but just more involved than what I need. I mostly just want a way to move messages back in forth. I don't need voice or video calls or anything like that.

One of the use cases Matrix was designed for is Internet of Things, so I think it's just fine for you.

Video calls come thanks to WebRTC in browsers, Matrix is just a transport protocol. I think it's quite light.

The newly released keybase chat supports this! It's not in the announcement, but malgorithms described the apis here: https://news.ycombinator.com/item?id=13600427

Idk about API-s, but tox.

WTF is the deal with tox? Seems like there are two factions, one which kinda seems to write code, and one that just complains about people stealing the project?