[orthodonticjake]

Does anyone use Mattermost? I remember thinking it wasn't too bad, and I guess it's open source.

[neom]

I mentioned them last week and per the comments I got, not really: https://news.ycombinator.com/item?id=46901946

[viraptor]

There's the mostlymatter fork which restores the proper oss behaviour https://framagit.org/framasoft/framateam/mostlymatter