Cross Team collaboration in Slack. Metateams!
CollabClub allows you to post questions to a metateam that spans multiple Slack groups. Cross Team collaboration. It also pulls in answers from StackOverflow right into your slack team. Very useful!
This was built for the Launch Hackathon 2015 and won the Slack prize.
If you have credits on your account you can offer a bounty for someone answering your question, and they'll gain those points on answering.