A few years ago I came across Ektron, who offer a popular and cost effective Web content management system (WCMS). I just found out that version 7.5 of CMS400.NET now offers Web 2.0 inspired social software-like capabilities including tagging, ratings, networking and blogging, etc. On the social networking side they describe it as follows:
"The new Social Networking Framework in Ektron CMS400.NET has been built from the ground up giving you, and your members, the most powerful toolkit of community-themed features making your site the place for people to meet, interact, and discover a new way to collaborate, find information and work together. Social networking is not just for your teenager anymore!"
Your very own Facebook? I really can't pass comment on the latest version of Ektron as I haven't looked at this latest version in detail (especially in such a crowded market of content management), but it might be worth considering if you're looking to quickly inject social computing features into your intranet or Internet site.