[SAGE] favorite open source knowledgebase?

["David N. Blank-Edelman" <dnb@ccs.neu.edu>]

Howdy-

Given the success of my last query, I'd thought I'd pester the collective
consciousness on another topic before I set out to build it from scratch.
This query is a little more ill-formed on the theory that if I cast a wide
net, I might get some interesting flotsam and jetsam along with the fish.
I've looked at the archives for the past two years and haven't seen quite
this question asked yet (interesting aside: one has to log in at sage.org
for last year's archive, but not this year's. Isn't the older info less
valuable?).

Here's the question: I'm looking for an open source system to provide a
self-serve knowledgebase for both my users and my staff. I'm not clear I
need a full-blown CMS (or that they are set up to provide all of the
following), but I'm open to suggestions from that realm as well.

I'd like something to help me round up internal documents like:

   - HOWTO documents (e.g. how to SSH tunnel)
   - FAQs
   - build instructions (i.e. how we built apache in our environment)

and serve them in the same interface.

I'd like to be able to apply arbitrary tags to the documents so I can serve
certain documents to certain user populations (e.g. staff, faculty) only and
collect it by subject (e.g. modems, wireless access). Built-in search
engine would be a big plus (otherwise it gets hard to enforce the notion
that certain documents only get seen by certain people).

Some nice touches would be:
 - the ability to have users comment on certain pages and have those
   comments be selectively added to the document for other people (ala Philip
   Greenspun's sites like photo.net) to see.
 - other tools to help with the documentation gardening process (e.g. 
   that helps us cull stale documentation, or forces us to look at all of the
   doc once a year lest it auto-expire). 
 - decent design/navigation (e.g. I'm not so keen on the FAQ-o-matic style)
 - ease of migrating existing docs
 - storage of docs in a format that let's me use them in another system
   later should we outgrow this one

I'm sure there's a ton of other features I haven't thought of for this sort
of thing. Does anyone have any suggestions on systems they are happy with 
that might address some or all of what I've mentioned?

Many thanks in advance.

           -- dNb