(I'm assuming everyone here knows what a wiki is, else shame on you :p)
I previously used kwiki on my site, purpletentacle.co.uk, but I found it really slow, and a mission to integrate into my site's existing design, so I wrote my own wiki engine in PHP, to solve both those problems.
This is a very light-weight wiki, it's just three pages - display.php (can duplicate), edit.php and save.php about 5K. It uses HTML as markup (language we all know) but it's easy to add your own (is some already). It can also do automatic archival of pages.
There's no styling or navigation in the package, so you can just copy it into your site's existing design - and hopefully into a WordPress 'static page'.
Anyway, everyone here is running PHP on a server, so if anyone could try it out and get back to me here, that'll be cool. I'd test it seperate from WordPress first.
ps. PHP 4 users have to uncomment some code, it's all explained.
pps. If my webserver is offline download from http://insidemdb.tripod.com/purple-t-wiki-v4.zip (get tripod.com referer)