Gollum[1] is really nice for that. It power's GitHub's wiki feature. All pages are in Git, and it supports several markup languages including MediaWiki but also Markdown, Textile, etc. Nice, clean interface, nice editing toolbar. Open source. Just clone the git repository where your pages are and run the "gollum" command to start up the server.
I have quite some math in my notes and like Gollum also for its integration with MathJax. I prefer the txt-based approach but a lot of math is more digestible when typeset properly so I switch between the txt and browser view.
(This is of course applicable to any txt-to-html based approach)
I've played around a bit with sputnik and its Git plugin a bit. It requires a webserver and a bit of configuration, but it stores its stuff in straight markdown.
1: https://github.com/github/gollum