fm project page
A general pluginterface
The main PHP script of ErfurtWiki contains everything necessary to run a wiki site (except the html around which make up your sites` layout). However at some point of its development the extensions got too large to be included into the core without hurting speed. So from now non-essential but powerful extensions can be added (using just PHPs include() statement) into the engine through the new pluginterface, which is surprisingly just a simple array structure listing the extension functions.
The mpi plugins
Another extension are the MpiPlugins which themselves utilize the general pluginterface to chain into the page transformation process to extend them with dynamically generated content.