I need a content management system where my visitors can login, preferably using Gravatar or any OpenID, and post questions. Admin or other users of my site must be able to log-in and answer those questions. It should have a thread format. Ratings of questions and answers are also preferable. It may be a separate CMS or plug-in/extensions for WordPress or Joomla. Please help me find a solution.
The WordPress Question and Answer Forum sounds just about exactly what you're looking to accomplish?
http://wordpress.org/extend/plugins/question-and-answer-forum/
Maybe that would accomplish what you're looking to do? I haven't used it, so can't voice for it myself but based on the description I believe users can post both questions and answers?
Hope that helps!
Thank you very much. I will have a look.