I like to try to put some sort of help system in my apps - either using the default Mac help menu, or rolling my own for iOS apps.
Producing the content for either approach usually involved writing lots of html, manually assigning links, then trying to massage the resulting files into a format which my app can display.
This is tricky enough for iOS, but almost impossible without resorting to the manual almost every time for the Mac - due to the Mac help browser's insistance on a particular format for the help files, extra tags in some of the html headers, and the need to add the right nodes to the app's plist.
I've previously used a comercial help editor - but that didn't help at all with integrating the output into my app, and an upgrade or two of MacOSX ago it just stopped working. It also had a nasty habit of deleting my work without warning.
So I've made my own. It's simple, and quick. It takes markdown, css and images, and writes out either plain HTML or a property formatted .help bundle for incorportation into your Mac app. It then tells you exactly what to add to your app's info.plist to integrate the help bundle.