I don't know of anything quite like Yedda, but if you are after a community driven website with interaction and the ability to build up a knowledge base I'd adopt a Wiki style approach with something like WetPaint or SocialText.  Both of these are wiki based, but also have good blog type facilities.  Wetpaint has a really nice interface, and a business model based on advertising, so it could provide you the website for free (apart from the effort involved in creating the structure and content).  I would recommend you check them out.  You could also develop something yourself with Joomla (straightforward) or Drupal (very flexible but complicated).  I've also seen this type of community site built using blog tools like Wordpress or Typepad.