Question2Answer - A Q&A site helps an online community to share knowledge.
Stack Overflow - Community-based Q&A part of the Stack Exchange platform.
OSQA - OSQA is the free, open source Q&A system you've been waiting for.
The Answer Bank - The Answer Bank is the UK’s leading question-and-answer site.
Askalot - Askalot is a next generation CQA (Community Question and Answer) system.
wikiHow - wikiHow is a wiki based collaboration to build the world’s largest, highest quality how to manual.