Cahoots! is an open source project that provides a Question and Answer forum that is driven by community participation. It also includes blogging, podcasting, and a knowledgebase functionality.
Logins are managed via OpenID, so you don’t have to worry about managing additional login credentials.
Your capabilities to create content are driven by “esteem”, which is a metric for tracking the response to content you provide. You can gain “esteem” by asking asking questions, posting blog entries, and having people follow your activities on the site. For more details on that, check out the about page.