RetroShare is a powerful tool which allows you to chat, share files and otherwise communicate with a group of trusted friends.
The program is what the developers call a "secure social network". The features are very similar, so you can share your news, read what's going on with other people, post on forums, use instant messaging and voice chat, share files, folders and more. But you're only connected to trusted friends/ family/ work colleagues (or whoever else you want to invite). So you have to explicitly add someone before you can connect to them at all. And because the system is decentralised - there's no central server control everything - and RetroShare's connections are encrypted with GPG (GNU Privacy Guard), you can be sure that no-one else will get to monitor what you're saying or sharing, not even the RetroShare developers.
If you're thinking this sounds a little complex to set up, then you have a point, to a degree. You'll need to generate a GPG key to establish your identity, for instance, then exchange it with friends to authenticate the connection. This isn't actually that difficult (creating a key is just a matter of filling in a form, for instance), and you only have to do it once, but it's undeniably more complicated than using Facebook.
And we found several other situations where RetroShare made few concessions to beginners. On first launch, for instance, it detects any plugins you've installed and asks you to authorise them, much like Firefox with a new extension. This is easy to do (it takes one click), but they just use an alarming "RetroShare has detected an unregistered plugin" apparent error message which will probably leave some users thinking there's a security issue.
This isn't quite as polished as regular social networks, then - but it's not really so difficult to use, either. A toolbar gives you easy to all RetroShare's key features, listing your friends, taking you to group chat rooms, displaying shared files, forums, channels and more. A left-hand panel includes links to common functions like the instant messenger, or file sharing, and a couple of wizards do a reasonable job of helping you get started.
Plainly RetroShare still isn't going to replace your other social network accounts. If you and a group of friends would like to also have a more private place, though, somewhere unmonitored, just for you, then it could work very well indeed. Just keep in mind that there will be quite an initial learning curve as you figure out how everything works.