I REALLY miss Phabricator, Scuba and (gasp) Tasks. Would love to have those back in industry. Far better than Github, Superset (?) and of course the dreadful Jira I have to use these days.
I was very impressed by Scuba's ability to ingest and search data... and very unimpressed by the interface. I found it terribly unintuitive, and often didn't get you what you wanted without having to run multiple queries.
Phabricator was pretty sweet... and the internal version of mercurial was a dream!