Over the past few months I've been asked about the range of Open Source Social Networking Tools, so I thought it might be an idea to put up a page which lists those that I know of with a brief description of each.
Drupal
Drupal is a general Content Management System, however with the use of a range of different third party modules, it can be turned into quite a decent "Social Networking" facility. If nothing else it integrates very well with other tools such as twitter, status.net, facebook, etc, etc.