It can be accessed through the Discord web client by just clicking on the link: https://discord.gg/eYqZMhm.
The Discord desktop client can be downloaded from the same link, or this one.
Discord, for those who don't know, is basically a text and voice chat platform that's become very popular recently. It has a web interface and a desktop client. It's a little bit weird to get used to, but it's very simple and for whatever reason attracts a much larger crowd than IRC or Skype does. Keep in mind I'm not proposing this as an official solution to the diaspora problem, but if enough people like it, I see no reason why it couldn't be at least a good adjunct to what we have already.
Why another communication medium? Well, why not? LessWrong itself doesn't really serve as a proper conversational locus, the IRC isn't doing much better, and the Facebook groups and Skype groups seem to be doing very badly.
Why Discord? Well, because that's where the people are at, plain and simple. I initially thought that Discord was just a gimmick -- yet another fad communication protocol and all that -- but after participating in it for a while and seeing the vibrance of the community that came from it, I figured that the most important thing is there being a critical mass of people to make discussion worthwhile. And Discord really isn't too bad of a protocol, to be honest!