I use pmwiki, after a long long search.
it's php only.
http://www.pmwiki.org/
no sql dependencies or such like.
it works on BSD 386 linux windows,
though it seems not to work on my new
AMD64 box. (I get blank pages, am investigating)
There is even a simple windows server, so you can put it on a stick
and carry it around with you.
which is nifty e.g. for work.