Open Atrium (http://www.openatrium.com) is best described as an "Intranet in a box" that sits atop Drupal 6. With the release of Open Atrium 1.0-beta4, Development Seed made a few crucial changes to the way OA is configured and structured. Now at beta7, there are still some older OA sites out there that are still running versions prior to beta4. Those sites require a little extra work to upgrade since they need to be upgraded to beta4 first, and then can be upgraded to beta7 and beyond.