This is cool and I'm excited to see more and more applications and services use WordPress as a platform.

A few alternatives have been mentioned in the comments, but no one mentioned Ning. They've been around a long time. The obvious conceptual difference is Ning isn't self hosted. I think Ning has changed hands a time or two. Their current pricing is insanely cheap, and likely not sustainable, but possibly something to consider... or not. :) There are some nice features there worth consideration.

Good luck with this, JJJ.