Aegir is a system for managing sites using Drupal and drush. We use it to manage this site in fact.
However, we use a fairly old version. As a precursor to doing some more work on the backup management I wanted to get my head around the new version of Aegir, and the object orientedness.
There's a really useful tutorial over on the Aegir community site:
That shows you how to add options to Aegir sites and pass the information into the backend.
The tutorial mentions a possible real life use of implementing HTTP basic authentication on a site...