Figment http://figment.com/
Museum Box http://museumbox.e2bn.org/
Padlet http://padlet.com/
Problem-Attic http://www.problem-attic.com/
Knowmia http://www.knowmia.com/
Flipasaurus http://flipasaurus.com/info/
Socrative http://www.socrative.com/
Remind 101 https://www.remind101.com/
SignUp Genius http://www.signupgenius.com/
Smore https://www.smore.com/
Voki http://www.voki.com/
Quia http://www.quia.com/
Class Dojo http://www.classdojo.com/