I just joined my third #slack team. They are popping up all over. I am now in one for the Rochester area Ingress Resistance, one for Recovering from Religion, and one for planning the BSides Rochester hacker con.
If you don't already know, Slack is a very well-built freemium service that combines multi-channel group chat with just enough document repository and project coordination functionality to be a really agile and easy-to-use solution for teamwork, removing barriers of geography and time.
You can start a Slack team in five minutes. You can have everyone connected in five more, if email invites aren't delayed. The free service alone is uncrippled, more than enough for fun. The standard offering is even free for non-profits.
I wonder how we used to do this. Email threads? Group BBSs? Yuck.