check out askbot - it's a Q&A forum like StackOverflow, but it's open source (python/django). Askbot supports PostgresQL and MySQL database backends and can be installed either from pypi (http://pypi.python.org/pypi/askbot) or github (http://github.com/ASKBOT/askbot-devel).

Demo and the meta site is http://askbot.org

Installation is quite simplified (has setup.py with dependencies).

Has some fun features - like ajax search and drill-down tag filtering.

Will be happy to hear your feedback.

Thanks.

Evgeny.