>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.