While I liked Michael Greb’s suggestion of trac, it seemed like an awful lot of work to set up, since I don’t currently use subversion and I have no idea how to set that up. So I went for an easier solution and installed TWiki. It seemed easy enough, except for the fact that it’s got two “Webs” devoted mostly to settings, tutorials and the like, Main and TWiki. It would make more sense to me if all that stuff was in one place and the main Web was free for you to edit as the main purpose of the site.
Maybe if I’d seen Jen’s comment earlier I would have tried DokuWiki instead. It seems to compare favourably if you look on WikiMatrix.
So anyway, the NavData Wiki is now set up here. So far one person has already found it and started to contribute, much to my surprise because it hadn’t been announced yet.