Posterous Spaces
I haven't had much of a chance to check it out yet, but if you're not already using Posterous, now would be a good time to start.
Whether you want to create a public blog, a private place to share family vacation photos or start a group for your classmates to stay in touch, you can create a Space for it. Adding members to your Space is a snap, and your members can participate through your Space's eb site, their mobile device or via email.
Read more about Posterous Spaces on the official blog.
