I'm looking for an open source knowledge base system that uses tags, rather than free-text search to identify articles (a lot like serverfault does).

I've looked at twiki, which many people suggested, but haven't found what I'm looking for. Basically I want to be able to create and tag articles, and provide an easy way for anonymous users to search based on tags.

Edit:

OK, here's some more detail regarding what I want. Basically, all the knowledge base systems I have seen so far are a collection of articles, each article with a title. Most of them allow you to categorise articles into groups and sub-groups. Users of the system can search for information using a title search, for example "How do I print from AwesomeProduct?" - which then shows a list of any articles that match that search text.

This is fine and dandy when your KB is for one version of the software product (the mythical AwesomeProduct ver 1.0). However, the development team then go ahead and create a new version (ver 2.0) that adds many new features and changes some existing features.

Now, how do we support both products in the same KB? The Naive method is to copy all articles from 1.0, and update them for 2.0, adding and removing articles in 2.0 as required. We can then add text at the top of every 1.0 article that says:

"this articles applies to 1.0 only, to see the 2.0 version, click here" (or something similar)

The problem with articles being indexed in the system by title is that it's very hard to filter based on meta-data like version. What happens when we create version 3.0 or 4.0?

The end-situation here is that you have a mess of articles. They're hard to search, hard to filter, and even harder to manage.

The solution (it seems to me) is to use tags, rather than text as the article index mechanism. So articles can be tagged with a tag representing the software version, topic area etc. etc. Users can then filter based on tag - an example search might be "version_1 printing" - which straight away gives a list of articles with all these tags.

So that's what I'm looking for - a KB system that uses tags, rather than text to index many articles. I'm sure I could build something with drupal, but I was hoping for something that worked out-of-the-box.