Pligg is an open source social publishing Content Management System (CMS) that can be used to create Digg-like social news websites. Pligg CMS provides the functionality of a social networking software that encourages visitors to register on your website so that they can submit content and connect with other users.

Pligg - Free Digg Clone
On Pligg powered websites stories are created and voted on by members, not website editors. Some features of Pligg includes user profiles, groups, private messaging, advanced comment system, RSS feeds and multiple languages. Moreover, the module system makes it possible to add additional functionality to your Pligg site withour altering the base code.
Pligg CMS is based on open source PHP and MySQL technologies that allow it to be installed on most web hosts. So, it is a perfect script for starting your own social news and networking community. Get this Digg clone today.