I have been using phpfox for a while now and I must say it is the destination especially for startups who intend to build platforms for social networking community.

Ability to build your own top-of-the-line professional grade social network. Beautiful lay-out and ability to customize style and features according to your community's needs. Well developed apps that faciliate communication among members. Friendly, curteous, professional and responsive customer support and guidance who make it easy to set-up and use.

PHPFox is very feature rich out of the box. Marketplace, blogs, forums, photos, groups, polls quizzes... the list goes on. It also serves as a solid content management system. There are plenty of tools to track and monitor site activity. Easy to deploy and install on web host server. Solid development backing from the developers PHPFox also provides the source code for both mobile and web applications at the highest licensing tier. Their customer support is spot on, even though there is an 8 hour time zone difference and all tickets are handled via an internal text based ticketing system