Most of the Social Network sites are not Open Source : FaceBook, Plaxo, MySpace, Last.fm, LinkedIn …
I searched for some and here is what I found so far :
- Mugshot is an open project sponsored by Red Hat.
- Elgg looks more like a CMS/blogging platform. But you have to install your own.
- Barnraiser the tools you need to take control of your identity and social network on the web. AROUNDMe is a suite of social tools; a social toolkit from which you can build your Internet identity, create networks and contribute to collaborative environments. Need to search more.
- The Appleseed Project is an effort to create open source Social Networking software that is based on a distributed model.
Obviously, it needs more work