It was only a matter of time before Facebook moved from social to work-based interactions. With the release of Facebook at Work they are directly competing with the likes of Slack - as with all new releases time will tell if people will move comfortably into this mode but I would think that as users are so comfortable with the interface that probably will catch on - does that kill Slack dead? Be interesting to see.
Facebook at Work functions in much the same way as competitors like Slack and Convo. While those services monetize with a subscription fee for data storage and group messaging between members, however, Facebook at Work is reportedly taking a slightly different approach