The full details can be found at the ProWiki site -- this includes a tutorial on the major concepts, some discussion of the internals, and a few initial characters from The Incredibly Dippy Subway Game, a micro-LARP set in Harvard Square Station, which is mainly an example of how to use ProWiki.
The basics, for those who are curious, is that this is a heavily enhanced version of UseModWiki, specifically designed for use with semi-structured data such as LARPs. (The explicit motivation for this project was to make Tabula Rasa III a little easier to write and track.) The primary innovation is the concept of properties -- named characteristics that a page can have. Properties can serve as data, holding arbitrary strings; they can also serve as links between pages, defining relationships between them.
Most of the interesting parts of ProWiki come in the form of queries: structured statements that allow you to generate the contents of Wiki pages based on the properties of those pages or others. There are queries that allow you enumerate pages based on their properties, queries that enumerate the properties on a specific page, and properties that act through inheritance. Yes, as part of all this I've added a very simple concept of inheritance between pages.
It's all quite rough-and-ready, as much a technology experiment as anything. But I think it should make Wikis far more useful for the sorts of purposes I have in mind, and I suspect that I've scarcely scratched the surface of the idea. If you want to really grok how it works, dig around in the sample game and look at what the page sources look like -- if you're used to normal Wiki technology, you'll probably be a bit surprised. Feel free to download the source and play with it, but be warned that this is all still very experimental code, and probably far from stable. Please do *not* edit the ProWiki site itself without asking me first. Thanks, and feel free to ask questions if you have them...