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.