SocialEngine - Socialengine PHP: Elevating Your Online Community Experience.
mooSocial - mooSocial is the best social network script to create a niche community or social site.
BuddyPress - WordPress social networking in a box.
Elgg - Opensource social network engine
EasySocial - Social Network For Joomla to grow your communities with the least time.
Open Social - Open Social is an out of the box solution for online communities based on Drupal 8.