Demo & support forum: http://wp3.in/questions/

AnsPress is the most complete question and answer system for WordPress. AnsPress is made with developers in mind, highly customizable. AnsPress provide an easy to use override system for theme. List of features:

• Sorting question and answer by many options.
• Ajax based form submissin
• Theme system
• Flag and moderate posts
• Voting on question and answer
• Question tags and categories
• Question labels (i.e. Open, close, duplicate) new labels can be added easily.
• Select best answer
• Comment on question and answer
• Private messaging system
• Point based permission (under development)
• reCaptcha
• User level : Participants, Editor, Moderator (in future it can be customised and you can add your own levels)
• Email notification
• User can add questions to his favorite
• User can edit profile
• User can upload cover photo
• Friends and followers system
• User points system (reputation)
• User ranking
• User badge
• User profile
• Pages : Tags, categories, users etc.