This would have been more interesting and innovative a couple years ago, but now that everyone and their mother (and grandmother, and grandfather) are on Facebook, I think Facebook Groups is a fine solution that offers all the features listed here.<p>I had this exact problem twice in the last month, and both times, I found that everyone in the two real-world groups I was trying to bring online was already on Facebook. Literally every single person out of maybe 50 people total, spanning age ranges from teenagers to folks in their late 50s. I found it much easier to get them to use it than it would have been if I had to explain this new posterous thing.