This is what I see groups for. Chat for small groups, Facebook groups for larger groups and long-form posts that require more in-depth discussion. This is what we do internally at Facebook and it works pretty well.
Basically we wanted the single threaded chatroom with people mentions, we didn't want web forums which is what groups are.
If FB@Work really wants to compete, they will eventually have to make the slack/irc style rooms app. I also think you guys use IRC right?
Other people who say lack of single threaded chat rooms is a feature, not a bug smell like apple saying you don't need X until they release it themselves. You of course can 'make do' with whatever communication medium you have, but for us we found the chatroom useful. Nobody ever used FB@work, while natural adoption for slack in the corporation was very fast.
TBH I think google is probably slacks biggest possible competitor. Google makes a pretty good set of business apps with gmail, calendar, contacts, docs, slides, spreadsheets, google drive, small group chats & video. A lot of big corps already use them. They just need to add corporate slack-style chatrooms and forums (not email lists/ groups) and they will probably take a chunk out of slack & co quickly.
Agree. I keep wondering when Google will release this Slack like chat app. We already use the other Google tools, and even Slack shells out to Hangouts for video.