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A Q&A site helps an online community to share knowledge. No matter what your area of interest, people with questions can get super answers fast. Question2Answer is a popular Q&A solution.

Askbot is a Q&A system, like StackOverflow, Yahoo Answers and some others. Askbot is based on code of CNPROG, originally created by Mike Chen and Sailing Cai and some code written for OSQA.

OSQA is the free, open source Q&A system you've been waiting for. Your OSQA site is more than just an FAQ page, it is a full-featured Q&A community. Users earn points and badges for useful participation, and everyone in the community wins.

Mamut is a tool that allows to ask questions and give answers and comment on both. In addition users could vote for questions and answers and mark solved questions as such.

Askalot is a next generation CQA (Community Question and Answer) system.