Organic Groups is social networking module for Drupal which allows you to have functionality similar to Yahoo Groups and Google Groups. In short, it lets you manage a group and all that you want to do with it - like send private and public messages, post public and private news, and interact with other members of your group with common social networking tools.

Organic Groups solves many common communications needs, like connecting geographically dispersed teams and creating niche online communities. 

We're experimenting with this functionality and are in the process of setting it up for our existing Interest Groups, as well as a closed group for the CVHL project team.