[support] Intranet

Hi all I have been told to establish a new intranet for the company that I work in and since we already have Drupal running our website/online store I think it would make sense to have it run the intranet as well. I have been researching the WWW and the Drupal community to find out how to get started. Perhaps there is a suitable module for this that we can easily add to a stand-alone Drupal installation and build from there? What is the most common way to get started with building an intranet in Drupal? Thanks in advance Rasmus F.