Here's a recent post by Gene Tognetti about using Web Walls for Collaborative Learning that appeared in SmartBlog Education's Tech Tips.
Padlet is the tool we wrote about, but there are other choices, as identified in this post by Richard Byrne on FreeTech4Teachers. LinoIt is another good choice. Primary Wall no longer exists.
Padlet - among others - now has an iPad app, too.
Hope you get some inspiration about how to add another easy to use tool supporting collaborative learning!