1. Blinkk – Blinkk is an application which combine digg, del.icio.us, and forum into a platform. View screenshot here.
  2. Vote up/down Package for Drupal – A plugin for Drupal CMS which can create a voting system which similar with digg.
  3. PHPDug – An open source digg-clone which support templates and has a very clean interface. It has several extra features such as automatically add stories from RSS feeds and multilingual support. View demo here.
  4. Vote It Up for WordPress – It is a WordPress plugin to create the voting system. It support the latest WordPress 2.5.
  5. Upwarded – Simple digg-clone application. But unfortunately i can’t found much information about it.
  6. Last but not least, Pligg – The most powerful digg-clone application which support templates and plugins. There are a lot of Pligg users, so i believe you can easily get support by the community.

http://www.techsnack.net/free-open-source-digg-clone-download