looking for a near-wiki

I'm looking for a script (free or commercial) that is similar to a wiki engine, without being 'wiki' per se. I want to be able to do nested categories and set group permissions for certain documents.

I'd also like to set some documents as open content-- editable by anyone who visits the site.

I've been considering everything engine and Brainstorm, but I guess I'm holding out for something that is maybe more developed, or that has a more intuitive front-end.

I'd prefer something written in perl or php, using either flat files or MySQL database.

Any help much appreciated.