These are summary notes of the presentations at Online Educa Berlin, 2014. If the text uses the first person, it is the presenter speaking, not me. We use MediaWiki, we use Discourse (discourse.com) - working with the organizers of these open learning courses (eg. billion in 2018. Introduction of Howard Rheingold. But wait.
However, your "free, open source" requirement presents a challenge. MediaWiki is probably the only one that I would recommend (as opposed to being *the only one* altogether) that fits both criteria and has the necessary maturity to suit real enterprise deployment. It's not hard, but does present a barrier to entry.
Last week I presented a session at ASTD TechKnowledge entitled eLearning 2.0 - Applications and Implications. Resources The following are resources that I provided as links in my presentation. It could just as easily have been called Web 2.0 Applications in Learning. Provide the content. I've embedded all the content from the slides.
They pair this with a wiki (using Mediawiki ) on their server where they collect “community knowledge The community practice is whomever asks the question, collects the answers then summarizes them on a wiki page. It was a great question so I happily shot off an answer in email. Anyway, here is the piece! That adds work.