Pligg is an open source CMS system that allows you to create your own  website like Digg, Readit etc in an hours.

Pligg is an open source Content Management System (CMS) that you can download and use for free. Pligg CMS provides social networking software that encourages visitors to register on your website so that they can submit content and connect with other users. Our software creates websites where stories are created and voted on by members, not website editors. Use Pligg content management system to start your own social networking community in minutes.

Pligg CMS is based on open source PHP and MySQL technologies that allow it to be installed on most web hosts on a relatively small budget. For support and free downloads please visit the Pligg Forum where you can find help 24 hours a day thanks to our excellent open source development team and community. Pligg CMS is a free software.

example http://www.pakblend.com

or got pligg website http://www.pligg.com/