OpenAtrium is built on top of Drupal, has a nice design and a useful set of features:

• Blog: A classic blog for each group that has commenting, file attachments on both the post and comments, and granular notifications.
• Calendar: A calendar that lets you quickly add events, suck in iCal and other calendar feeds, and support single or multi-day events.
• Group Dashboard: Mini widgets give you a snapshot of all the activity happening across your groups.
• Documents: A simple online handbook that lets you collaborate on documents, store and compare revisions, attach files, and once you're done print out the final copy.
• Shoutbox: Kind of like a private twitter, the shoutbox lets you share short messages, links, and information with just the people in your group.
• Case Tracker: A full ticketing system that lets you assign to do's and create unlimited projects within each of your groups. The case tracker also lets you classify the to do, give it a priority, and manage its status.

For small companies, it is an efficient tool to create/maintain an intranet.