IT Documentation Platforms [closed]

I know that this isn't free, but I think the Altassian products could suit your needs. Specifically the Confluence Wiki could help with your documentation and the JIRA module could do issue/bug tracking.

Not to over simplify, but Sharepoint comes to mind.

Personally I'd go for a either a wiki (I like Trac), or Plone.

At a previous employer, we used Plone for an internal KB application whereby Support had certain r/w permissions, management had others, and development had yet another.

Jira and Confluence are very interesting for this, as SLY mentioned. On the free end, you'd have Trac and it's relevant plugins which comes to mind as well.

Then again you are looking for a free Kitchen Sink, and none of those recommended so far will provide all of the desired functionality.

If you do have a few extra cycles you can free up for this, Trac is extensible via plugins so you may be add some of the functionality you need.

I also see a wiki as being the best fit for your requirements. Wikipedia has a very good comparison of wiki software with features, target audience and licensing/cost etc., so you might take a look there in addition to the recommendations in the other answers.