Elgg
From the official Elgg website:
Elgg is an open source social platform based around choice, flexibility and openness: a system that firmly places individuals at the center of their activities.
Your users have the freedom to incorporate all their favorite tools within one environment and showcase their content with as many or as few people as they choose, all within a social networking site that you control.
To learn more about this Community solution and all the other Community solutions that Wallanet offers go here: http://www.wallanet.com/open_source_packages/community
Price: $0.00