Question2Answer - A Q&A site helps an online community to share knowledge.
The Answer Bank - The Answer Bank is the UK’s leading question-and-answer site.
AnswersLOG - AnswersLog is a question-answer platform that provides unique features to help you to give answers to your questions in better ways and make your content more popular.
Stack Overflow - Community-based Q&A part of the Stack Exchange platform.
Ask Me Help Desk - Ask Me Help Desk is a question-and-answer site.
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.