Padlet (formerly known as WallWisher) is a great tool for digital collaboration activities such as brainstorming, KWLs, etc. A recent post on FreeTech4Teachers highlights some creative ways to use Padlet in the classroom:
http://www.freetech4teachers.com/2014/09/5-ideas-for-using-padlet-in-school.html#.VClXz_ldW8A
http://www.freetech4teachers.com/2014/09/5-ideas-for-using-padlet-in-school.html#.VClXz_ldW8A