Open Source Social Networking with Elgg
Elgg is a fairly mature, distributed open source social networking application (you can install it on your own server, and your users can connect with those on other servers as well).
A roadmap for Elgg 1.0 has recently been posted:
“To date, Elgg has been a great tool for creating a web-based social network. It was the first social networking platform to include OpenID support, and through its support of standards like RSS, FOAF and XML-RPC, as well as its highly extensible architecture, provides functionality unique to the market. If you want MySpace in a box, you can do it with Elgg; if you want a customised network with functionality specific to your niche requirements, you can do that too.
“Elgg 1.0 takes this flexibility as a starting point and supercharges it… Elgg 1.0 acts as a social application engine; a way to power any socially-aware application, whether it’s on the web or not.”
Elgg has a few open source competitors I know about, including NoseRub and Appleseed. There’s also some other related tools and protocols like OpenID that offer the possibility of the entire web becoming socially-enabled in the future (which I think is inevitable, in fact).
However, Elgg has already been very strong in providing self-hosted social networking sites used by several large UK universities, and seems to be the most complete of the above competitors.
Here’s my profile on Elgg.