I've been adding new modules to an instance of Drupal we're working with where I work. Organic Groups allows you to essentially set up private sub-sites within an existing site. It can even have its own theme (look and feel). PingVision--a company we're pretty interested in right now--mentioned it in a recent meeting. It is potentially a powerful tool in mananging projects from different clients in a single environment. Coupled with Project and some of Project's add on modules, you effectively have a bug management and project management tool.

I continue to marvel at what a versatile tool Drupal is.