In a Nutshell
Buddypress is a WordPress based social network plugin, which is extremely easy to install and use. It’s free. As in beer.
Get it here: buddypress.org
What it does
Buddypress is a plugin for WordPress, the most popular (and free) blogging software and CMS. What does it do? It basically provides all the functionality you’ve come to love in a social network (yeah, like Facebook). Profile pages, groups, a stream of activity. It’s all there.
What can you use it for? Well, if you’re a company who wants an internal social network, or a small college or simply a group of friends or a family who wants to connect privately. It’s really quite up to you, the possibilities are more or less endless.
It’s a WordPress plugin, so before you can set it up, you’ll have to have a working WordPress instance set up. There’s a small review of the software right here, for help on installing it (it’s really very easy) see this page.
Once you’ve got WordPress up, it’s really just a matter of installing the Buddypress plugin via the built-in plugin-system. One-click install and you’re done. All the settings of the networking functionality can then be changed from within the WordPress dashboard, there’s themes to change the layout, if you’re unhappy about the basic aesthetics.
If you want to see what a basic installation of Buddypress looks like, have a look at their demo site: testbp.org
Buddypress is free. You will need a WordPress installation and ideally your own domain name.