AskBot - Askbot enables users to create Q&A forums.
The Answer Bank - The Answer Bank is the UK’s leading question-and-answer site.
Ask Me Help Desk - Ask Me Help Desk is a question-and-answer site.
OSQA - OSQA is the free, open source Q&A system you've been waiting for.
Blurtit - Blurtit is a Q&A website. You can ask a question or answer on any question.
Scoold - An open-source, enterprise-friendly Q&A platform inspired by Stack Overflow.