my baby's in the white fluffy clouds

ikiwiki (http://ikiwiki.info) is kind of that -- it's is a wiki backed by Your Favorite Version Control System, so it's easy to keep a working copy where you need it, net or no net. Doesn't necessarily get you something you can browse locally with a web browser, but it may be enough for your purposes. I've been using it to run my main web site, actually. Being able to publish a blog post by committing and 'git push'ing is really awesome. :-)