Hi Joel,
Please do not post these names.
We looked at Drupal Commons, OpenSocial (early version), OpenAtrium, SharePoint and I think one or two others. There were a number of reasons, but the primary was the level of foundational development work which was needed to have any hope of attracting and retaining members through core functionality and features.
Hey, I loved your article on providing true value to Members. Good job on your thought-leadership and good writing, too. I wholeheartedly agree.
Phil