Buddypress

The book I read to research this post was Buddypress for Dummies by Lisa Sabin-Wilson which is a very good book which I bought from Kindle. Automattic is the organisation that makes Buddypress as well as Wordpress. As you probably know Wordpress is a blogging tool. Buddypress is an open source plug in for Wordpress that turns it into a social network site. It only works with Wordpress MU which is the multi user version. This also means you need a server although you can use a hosting company like GoDaddy. You also need MySQL & PHP installed & also probably a version of Linux. There's easier solutions like Ning where the hosting is done for you & it might be worth looking at my post on Ning at
http://scratbag.me/
I also have a post on Wordpress at that site.
The idea behind Buddypress is you can have niche social networks. People can go to these sites & meet people with similiar interests. They can also join forums & do blogs at these sites. One application of Buddypress at their website is that schools often use it to start their own social networks. It gives the parents peace of mind & is easier to police than if a child joins Facebook. Although Facebook has a minimum age limit there are ways around it. Finally if you start a niche social network you have to be prepared to go around sites like YouTube & social bookmarking sites looking for information to put on your site. That's in addition to jobs like having to welcome new members & answering messages. A lot of people hopefully will visit your site daily & they will expect there to be fresh content.