ikiwiki is the engine behind this wiki and several others I run. It has a wiki of its own at http://ikiwiki.info/.
I wrote it after being unable to find a wiki that had all the features I wanted (most notably, subversion backend, markdown syntax, and hierarchical subpages). My first blog entry listing my requirements resulted in a suprising lot of feedback, and after looking at a lot of wikis, I blogged about my decision to write my own.
It's written in perl just because I am highly proficient at writing good and effective perl. People who this bothers somehow will be ignored.