I'm an enthusiastic 'Tavi user and hacker. Tavi is my PHP wiki engine of choice, because it is not bloated, simple enough to be easily modified, and yet it offers all the usual wiki functionality.

My pet 'Tavi project is the [Blackbox site], which is based on a heavily modified 'Tavi 0.25.

You can find more information about the Blackbox-Tavi version on the following page (including where you can download it): http://blackboxwm.sourceforge.net/AboutTheWebsite

You can find patches for some of the functionality in the Blackbox-Tavi on TaviPatches. Here's a list of patches I've submitted so far: