I have just started toying with OpenClass, a free LMS (learning management system) from Pearson, which is a Google Apps for Education tool. It's quite capable, yet basic at the same time. It reflects a certain structured class setup, without much obvious room for flexibility. There seems to be some social features like the class wall, but it's difficult to assess how collaborative students will be able to be. It seems like Google Docs are well integrated, which could help, but what about discussion boards, wikis, etc?
I think this is a useful free tool to start with, but is likely yet to compete with Moodle, Blackboad, HaikuLMS, and the like.