Well, happy users since around 2015 (?).

There is a catch though - we use it only as a code review platform. It always seemed to be focused on that part more than in any other. I'm not saying everything else is bad, it just a gut feeling that code review always got the maximum attention.

And another catch is that it seems they lost their momentum even in this area. I recall times when we waited for weekly status update to see if there is something we'd have as excuse for an upgrade. Now it's even not a weekly update and speed of development seems to be slow.

The Wikimedia project and some other high profile projects use it.

I did a pretty thorough evaluation once which included Phrabricator, it came out very well, especially the work flow around code review. It wasn't chosen for unrelated reasons.

I don't know why it isn't more popular than it is. It seems to be very mature, certainly better than a lot of tools that organizations pay good money for.

There's no one pushing phrabricator. No marketing means that most of the people picking a tool to use have never even heard of it, and it's not really something that a single developer can adopt and then champion internally.

FreeBSD is probably one of the most visible users of Phabricator.