Developing and customizing social networking software can be incredibly easy, using open source programming languages like PHP and Ruby on Rails. Here are some of the Internet's best offerings for open source social network tools.
Winner of Infoworld's best open source social networking platform of 2008. Not a bad endorsement.
One of the best things about Elgg is its easy plugin-in based widgets and additions. Want a new feature? Just check out the plugin database. If what you need isn't there? Well, you can always develop your own and put it up in the plugin database yourself. At any rate, it has plenty of odds and ends available for use, so chances are that you won't have to do any coding if you don't want to.
Elgg puts more emphasis on the individual at the center of the social network, as opposed to a more amorphous, cloudlike view of social interactions. The individual user can customize their own page and profile to a considerable degree, though the developer still has ultimate control.
Elgg may be viewed in many formats, including on most cell phones and iPhones, and is built primarily of LAMP, including MySQL and PHP.
Possibly the most popular of these choices, and is built on PHP and MySQL. In addition to being a generally universal social networking tool, Dolphin also has some unique features that many other such softwares have difficulty with, such as streaming video chat and an integrated billing system.
Be warned, however: while Dolphin is free to use and download, it costs money to have the ad module removed from the code.
As the name implies, PHPizabi is based primarily PHP and MySQL. While it has basic social networking features, it isn't quite as rich as Elgg. It does, however, have support for a variety of languages, as well as easy integration with blogs and forums. PHPizabi works better for small networks than for large.
Anahita is built off of Joomla!, using Nooku.
What makes Anahita different is its sheer scalability: it can manage as big or small of a network as you want. It also supports OpenID and can be integrated with cloud computing resources such as Amazon Cloud Storage for space efficiency.
Be careful, however, as just because this one is open source does not mean that it is free. There are a few fees slipped in here and there, especially with regards to the membership that is required to utilize many of their tools. Without this membership, Anahita remains quite bare boned with a minimum of social networking tools at your disposal.
LOVD By Less
Sweet and simple, this program doesn't have all the bells and whistles as many other applications. This does not translate into a minimalistic experience, however, as the social networking possibilities are more than enough to keep you occupied—without throwing in those resource-intensive features that you probably won't use. Available features include blogs, photo galleries, activity updates and user messaging.
LOVD By Less is built with Ruby On Rails, one of the few social networking platforms to do so.
Another plug-in based social networking tool, BuddyPress specializes for use in Wordpress, and it serves this purpose well. It can turn any blog into a fully serviced open source social network with ease.
Unlike many of the above, Mahara caters more towards creating social networking for purposes of building and displaying a portfolio more than anything. This means that a circle of friends using a Mahara-based network are more likely to be sharing learning via informative blog posts than chatting about what they saw at the supermarket today. This degree of professionalism, however, does not get in the way of the whole social aspect of it, as all the usual friend mechanisms are in place. Mahara runs on LAMP.
For a comprehensive overview of open source and social media, check out this article.
For more information, there are a variety of other listings of open source social networking and open source social network tools. New projects are being created all the time, so if none of these seem to suit you, if you have the patience, simply wait around—or code it yourself! One of the most complete listings is Vivalogo's Top 40 Open Source Social Networking Software.