This is Askbot project - open source Q&A system, like StackOverflow, Yahoo Answers and some others
Demo site is http://askbot.org
All documentation is in the directory askbot/doc
askbot-devel repository is open to anyone who wants to help develop Askbot - just drop us a note
Askbot is based on code of CNPROG, originally created by Mike Chen and Sailing Cai and some code written for OSQA