Ægir is a new set of contributed modules for Drupal that aims to solve the problem of managing a large number of Drupal sites. It does this by providing you with a simple Drupal based hosting front end for your entire network of sites. To deploy a new site you simply have to create a new Site node. To backup or upgrade sites, you simply manage your site nodes as you would any other node.
We are using Aegir to manage sites like our Open Atrium cluster. Will White has a great screencast showing Aegir in action.
In Norse mythology, Ægir was the god of the oceans and if Drupal is a drop of water, Ægir is the deity of large bodies of water. To learn more about Aegir, visit http://groups.drupal.org/aegir/overview.