If you wanted examples of other sites running Q2A, check here: http://www.question2answer.org/directory.php
The other popular software is OSQA (runs on Python/Django, not PHP), here's a list of their sites: http://meta.osqa.net/questions/12/what-sites-are-running-osqa
I don't think there are any others remotely close to these 2 apps.
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