Share 'Open Source Learning Platforms'

I'm just beginning to research OS learning platforms. There are a few that I will be doing a comparative analysis on over the next few months:- 1. Moodle 2. Sakai 3. Plone (although that's more of a content management system - CMS) 4. Drupal If anyone has used these platforms I'd appreciate feedback on their pros and cons. I want to use open source as much as possible for both the cost and th…