Mamute
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. A prominent example is Stack Overflow.
Askalot
Askalot is a next generation CQA (Community Question and Answer) system.
AskBot
Askbot is a Q&A system, like StackOverflow, Yahoo Answers and some others. Askbot is based on code of CNPROG, originally c ...
LampCMS
LampCMS is an full-featured Open Source Question and Answers web program written in PHP with deep integration with Facebook, T ...
Stack Exchange
Stack Exchange is a fast-growing network of 84 [and counting] question and answer sites on diverse topics from software progra ...