I’ve shared Wallwisher before (it’s what we used to gather ideas for last June’s Edcamp), but I hadn’t looked at it recently. They’ve updated the site and it’s even better than before. You can get started with one click (and later set the wall to private if you’d like by creating an account) and easily add text, links, images, and other files to your wall simply by dragging and dropping the files.
Wallwisher even works great on the iPad now, too!
Wallwisher is a great tool for students to gather ideas and questions on a topic. I’ve heard from lots of teachers who use it as a formative assessment tool.