HipChat, while providing the XMPP backend, and a self-hosted option, isn't cheap, and doesn't seem to provide the extensibility that an open source option would. But, it's certainly closer to the right thing than Slack (at least, from a surface level examination).

I guess it doesn't even need to be XMPP, specifically. But, some open standard and some level of interoperability would be nice. In googling I came upon matrix.org, which also seems promising, but has the same problem XMPP has of not having great clients (though I also found Kaiwa, which looks like a pretty good XMPP client with Slack-like features). Maybe one of these open source projects will formalize their protocol, and we can all move forward on interop with that.

[Matrix lead here] The open source clients for both Matrix and XMPP are improving a lot currently. On the Matrix side there's vector.im; on XMPP there's Kaiwa and Conversations.im. If you want to help break the fragmentation and have an open standards based approach please run the clients and help us make them better - it is open source, after all!

Something really missing about matrix (at least last time I looked) is a hosted option with my own domain.

I don't want to use the domain you provide, because I'm tied to a provider forever. I don't want to set up my server right now, because it's just too much work to try something that I may end up dumping (because nobody else I know uses it yet).

The overhead to get it is too high, when you're just betting it'll prosper.

Yup, agreed. We're planning to provide domain vhosting (ie point the SRV for your domain to matrix.org and you'll get your own server instance) which should help a bit, although doing that for free could start to get uneconomic. We also need to work out a nice way to let users migrate between providers.

Free for "2 users per domain" might catch on for those of us who use our own domain for email/im. Not the most common thing in the world, but probably quite common amongst your potential early adopters. All while keeping away domains with hundreds of users that would cripple your servers.

Jebus. That chart is horribly depressing.

That chart is amazing (and depressing, as another commenter said). I counted and I've used 18 different ones. I've also used a few others for video and audio conferencing, like WebEx (unless that falls under a particular Cisco one in the chart, I don't know).

Currently I'm "only" using Slack, Skype, iMessage, and Google+ Hangouts (very occasionally, with considerable loathing).

It strikes me the situation is inherently ridiculous, but after not far off 20 years of dealing with it, I can't say it bothers me that much anymore.

Needs to be updated. It shows Zulip died in late 2014.