Introducing EMO Questalk Pro - the pinnacle of question and answer plugins for WordPress.
Demo: https://codecanyon.net/item/emo-questalk-pro-your-ultimate-question-answer-wordpress-plugin/15057949
DW Question & Answer Pro is a WordPress plugin for creating categories or fully functional Q&A sites such as StackOverflow, Yahoo Answers or Mail.ru Answers.
QXAPHP - social platform, which allow users to ask and answer in topics which they are interested in. Application is build in PHP under MVC structure.
Demo: https://www.codester.com/items/11084/qxaphp-social-question-and-answer-platform-php