We all love to hate our Facebooks and Google plusses, but here is something which puts you firmly in control of your own data: Diaspora. It's an open source peer-to-peer social network. If you wanted to, you could host your own data on your own server, and it would still integrate seamlessly into the overall network. You can even move your data around different hosts as needed.
Amazing to see this come together. Especially if you consider this started out as the work of four enthousiastic developers (Daniel Grippi, Maxwell Salzberg, Raphael Sofaer,
Ilya Zhitomirskiy) over the course of one summer. And it's all built in Ruby on Rails.
For the software developer geeks, there is also a blog which is presenting some of the design that went into Diaspora. Here, for instance, is a discussion of how the different users get connected in this peer-to-peer setup.