It didn't have to be this one; anything that met the following five criteria would've worked:
I surveyed the handmade community, and these are the core desires that bubbled to the surface. Stable services like Slack, Gitter, rocket.chat, and IRCCloud are awesome but don't simultaneously meet all five criteria, or they are gated with per-user pricing. That is prohibitively expensive; we're a community, not a small team.
Mattermost satisfies the community's five requirements and is conveniently FOSS; it also has a web client and a desktop app. The Handmade Dev Team believes everyone will be at least not-angry with this solution, and I personally enjoy it. We're working towards login credentials to be the same as the website, too!
Expect an update from Jeroen as to how to access the new community chat, once it's ready.