BuddyPress.org

By the way, just in case you are not aware, there are a few high-profile business-based sites that are using BuddyPress–at least some of BP’s components. For instance, http://pro.gigaom.com/ has integrated BP, although it does not have all the components enabled.

The main reason I switched to BP (this is a continuation of a post I made on another thread) is because of the potential I saw in it as a platform to build robust, serious, social-based business platforms.