I would explain this plugin, but the creator of it does it much better than I:
Friends RSS Aggregator (FRA) WordPress plugin was built to enable a WordPress installation to have a livejournal.com-like friends page. By creating a group of friends’ weblog links with RSS/Atom URIs in a particular link category, a user can display an aggregated list of posts by date or name. The word ‘Friends’ in the plugin is also a bit of a misnomer since the plugin is by no means limited to aggregating just friends’ weblogs; FRA allows aggregation of any group of links (that specify RSS URIs) in a link category.
Have a look at the Project Page for more information.