This add-on allows you setup forums based on Question & Answers with just a few clicks. Also, allow users to ask questions while other users are able to answer the question with multiple. Then, the question starter may then mark which answer fits best.

Questions & Answers Forum allows you to turn your forum into a knowledge base, support portal, or just a questionnaire based community. Also, you can choose which forums are QA based or add a custom widget that allows your users to see which threads are unanswered.