Open Source Options

Alternatives to Stack Exchange - [1]
Question2Answer - Godot engine uses it. [2]. Looks pretty good - has vote and widgets; Wordpress integration. FB login.

OSE Needs

Note that the 2 critical aspects of a Q&A site that OSE needs is:

Upvoting - this distills wisdom to the top, with inherent limitation of answers being as good as the audience. With a quality and sizeable audience, as well as great management, this could fuel collective genius.
Embedding of individual questions. Imagine embedding upvote capacity anywhere on the wiki or on the blog.