Pligg – Free and open-source CMS for social publishing

Pligg (now called Kliqqi) is a free and open-source content management system (CMS) developed by yankidank (Eric Heikkinen) in 2005, based on PHP and MySQL. It offers a set of features that are similar to popular social publishing websites like Digg or Reddit, where users can submit and vote on news articles and connect with other users.