I recently started exploring FitNesse for the first time. This began when someone pointed out the relatively new Slim protocol for using Fit tests with Systems Under Test. The primary benefit of Slim, as seen in the diagram below, is reducing the footprint of the framework in the SUT, and sharing a single implementation of the table interpreter. Improvements to the Fit interpreter do not have to be duplicated across multiple Fit implementations by multiple Fit f/w implementors.
I enjoy learning about various wiki implementations, generally. And FitNesse as a wiki has some interesting features. Mostly these seem geared toward supporting the wiki as a home for tests for multiple projects and multiple developers. I am always torn between the simplest wiki structures, such as the original c2 flat namespace, and structures such as confluence's spaces and hierarchies.
FitNesse has its own (as far as I know, unique) structure of subwikis. Essentially any page can begin its own sub-hierarchy, and the page name syntax allows for navigating and searching across the hierarchies above and below. This seems like a good thing, but I've not really used it yet.
Since I'd like a Fit tool for some fun projects, but I don't have modern Fit tools in the languages I'm using, Slim is the quickest path, and the whole FitNesse wiki comes along for free. I'd done a wee bit of integrating Fit and confluence along with http://twitter.com/ecopony and Slim FitNesse holds more promise for less effort.