Wallwisher is a simple collaboration tool that allows you to create a "wall" where students can post 140 character "stickies" on the wall for all to see. It's a dynamic tool that can be used for brainstorming, reaction to a reading, exit slips, feedback, or various other ways. As the creator of a wall, you are also able to moderate what gets posted and what does not. For more ideas on how to use Wallwisher, check out this presentation for ideas. I used it last year as a way for my students in my AP Economics class to leave suggestions on how to survive AP Econ. That example can be found here. For examples of how other colleagues are using it, check out high school English teacher Nora Bowers' example.
If you have any questions, you can find me on Twitter @jjanczak