Document Management CentOS

Can anyone recommend a good Linux document management system?
I don't really need anything fancy.  I would rather have simplicity.
I don't need really to check out documents, etc.  I just want something
simple that shows a web page like


- Requirements
   - Customer Requirements
      - Bill Gates
      - Albert Einstein
      - Paris Hilton
   - Test Plans
      - Project 1
      - Project 2
      - Project 3
   - Design Documents
     - Smokeless ashtray
     - Light-free flashlight
     - Peel-free apple
     - Pet Projects
       - OHare Expansion
       - Etc.

This is similar to the Windows explorer.  If an item has a + next to it, it can be expanded.  If it has a - like above it can be
collapsed.  When you get to a bottom node (e.g. "Smokeless ashtray") clicking on that will let you download a document
for that item.

I also want authors to be able to replace documents with newer versions (i.e., there is a new requirements document
for Paris Hilton for instance).

I guess a simple directory structure with no index.html files might work, but it would show only one directory at a time.
Anyone suggest anything? I found "Simple Groupware" but it is awfully complicated and I can't figure out how to change
the directory tree structure.  I also found Document_Library but it won't build and complains something about python not
being able to find a recipe for an egg.

Any suggestions?  If worst somes to worst I can just make a simple web page with DIV which goes unseen if you click
on it.