Long time Mac users will fondly remember ClickBook as a handy utility that debuted on the Mac, was shuffled from company to company, and eventually languished in favor of the Windows version. Well, the current owner, Blue Squirrel, has released a Mac OS X version.
I don't have a lot of faith in it, however, when I find that the link on their website to peruse the HTML-version of the manual won't load in the latest version of Safari. Sort of makes one wonder how carefully they're paying attention, eh?
In the absence of ClickBook, I've been using the free CocoaBooklet instead, by the way. Not nearly as full-featured, but it's free, and Mac OS X-savvy.