Glogster is a private and safe student environment where students create interactive posters. The Free Basic account allows students to create and share glogs but lacks many tools in the premium level. The Teacher's premium licence for 200 students costs $99 per year.
Scribblar is a free multi-user whiteboard that allows for brainstorming and collaboration. It has text-chat and works in all browsers.
I plan to use it to have students create a review for the properties of quadrilaterals.
Part I: Defining the Need for Change
Part II: The Key Elements of 21st Century Learning
Part III: Implementing 21st century Skills: 9 Steps to Build Momentum