Drupal Commons
Drupal Commons is a Drupal distribution billed as “social business software.” That means that (commercial open source company) Acquia is distributing Drupal bundled with some other modules preconfigured to work as a company’s interactive user-facing website.
The result is a solid starting point for large businesses to make the transition to building relationships with their customers over the internet. Drupal Commons provides a fairly complete business-oriented community structure out of the box.
Drupal Commons revolves around Organic Groups. A Commons-based website essentially consists of a bunch of groups, each of which can have their own forums, wikis, blogs, documents, polls, and activity stream. There are also userpoints, email notifications, bookmarks, user relationships, and a WYSIWYG editor (CKEditor, to be precise). Users and groups have pretty comprehensive dashboards that can be customized by administrators.
-- From Mediacurrent review
Drupal Commons is free and open source like any Drupal, you can install modules and themes like any Drupal 6, though there appears to be menus etc in the drupal commons that will have to be replicated by oneself in one's own skin.
Setup
Drupal Commons is set up as a standard Drupal 6.
