One of the reasons I like Dokuwiki and use it for my team is the fact that it stores everything in .txt files.
You get to use wiki formatting and the features that wikis give you that text files don't (linking between related pages, etc), but it's still just a script writing to .txt files in a human-readable format. No lock-in and no database to worry about configuring or recovering from a crash.
I'm using MoinMoin, which I also like because it stores its data in text files. MoinMoin has a "personal wiki" configuration that requires hardly any configuration and runs its own built-in web server. It also has a full-blown wiki with user IDs, access control lists, etc. that you can run under Apache or other web servers. I'm using it at work to store some documentation for my work group. (http://moinmo.in)
You get to use wiki formatting and the features that wikis give you that text files don't (linking between related pages, etc), but it's still just a script writing to .txt files in a human-readable format. No lock-in and no database to worry about configuring or recovering from a crash.