The External Help module makes it easier for other modules to add links to external help pages, complementing description texts and help files. The audience of this module is purely other modules – no user interface is provided.
Why this module?
There is already Advanced Help out there, and you can write whatever you like in description texts. So why use this module?
This module supports the idea that it makes sense to have module documentation on drupal.org, in contrast to having it in-code with the module. This makes it possible to find, read and improve documentation without having to install modules and/or write patches.
The idea of this module is to make it easier to link to external help pages in a consistent way, and having all the external help pages listed in one place in the module code – making it easier to maintain them.
This module is also inspired by the discussions about having inline help texts imported from drupal.org, similarly to how translations are imported, thereby allowing updates and improvements without having to change core. This module, however, doesn't go very far in trying to solve that problem. (For more information on this issue, see http://drupal.org/node/1031972 and http://drupal.org/node/1291058.)