The advanced help module allows module developers to store their help outside the module system, in pure .html files. The files can be easily translated simply by copying them into the right translations directory. The entire system can appear in a popup or not as the module prefers (and by taking away access to view the popups, a site can force the popups to not exist).
The system ties into Drupal's search system and is fully indexed, so the entire contents can be searched for keywords. the help files can be placed in a hierarchy as well, allowing for top down navigation of the help.
By itself, this module doesn't do much; it requires another module to support it, but it does come with a nice little sample of text from Wikipedia to demonstrate the system.