Question2Answer - A Q&A site helps an online community to share knowledge.
Stack Overflow - Community-based Q&A part of the Stack Exchange platform.
The Answer Bank - The Answer Bank is the UK’s leading question-and-answer site.
Blurtit - Blurtit is a Q&A website. You can ask a question or answer on any question.
Askalot - Askalot is a next generation CQA (Community Question and Answer) system.
Ask Me Help Desk - Ask Me Help Desk is a question-and-answer site.