I discovered PmWiki while looking for a convenient way to manage a flexible website. My requirements were that the website should allow for easy page and links addon, offer the possibility to visitors to contribute via creating their own pages, and allow non-experts to update the content easily.
With a few tweaks, PmWiki allowed exactly this. I was impressed by the clarity of the code that allowed adjustments to be made in no time, considering the fact that I'm no PHP guru to begin with.
Some of the best features I found on PmWiki:
The result available here(approve links), it's a french website about a role playing game I created.
On my TODO list: