Keeping in mind that I havent tested all the features and functions of the one that you linked to, however, I think I have seen something like that before being sold on this forum, its like some social script, and I think it was $2k for the base, and the site owner would have modified it on top of that. I did a quick search but couldnt find what I was looking for, but did find this cheaper and nasty one: http://turnkey.org/scripts/community/index.php and you just take that and modify it. Just keep going into google, and searching for different social scripts.
well when i first heard about the site they had 6 million users, they have over 30 million now they say in a year and a phone app.