As for DokuWiki, PmWiki is based on a flat file system but they are not ".txt" files and so far I haven't found it easy to edit them locally on my PC. However, editing on the web is a breeze with a nifty interface that allows push-button entry of the wiki markup.

The URL rewriting is camel case (mixed upper and lower case or a capital at the start of each word) and works very effectively.
Categories can be created easily using the URL rewrite system. By default the pages are /Main/PageName but it is also easy to generate categories so the path could be /FAQ/Index for example.

I am yet to explore the group access control or control of individual pages but using a provided htaccess example file and a user auth php file it is very simple to implement read only access. The system also comes with a built in way to generate an MD5 encrypted password so locking the site for admin access is quite simple.

I have noticed an RSS file in the distribution but need to look further into this capability.

One thing I especially like is the side bar navigation and a variety of skins that are readily available. I have "lean skin" installed here.

In that regard I will look at implementing a side bar in the template in DokuWiki also.