Slack is a glorified chat, but everyone who used IRC 20 years know that a channel based chat was an efficient tool even back then, and as it still is, so so is Slack.

The real challenge with it is that it does very poorly what Outlook does well: giving a good overview to everything. When your volume of messages reaches around a hundred a day, you cant keep track anymore, and start missing out, which is unacceptable in an working environment.

Our approach at http://www.collaborationobjects.com was to take the good from Outlook & Social, do check it out if interested.