Vuukle - Vuukle is a multi-point user engagement platform.
Padlet - Visual boards for organizing anything.
DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
BookWidgets - BookWidgets is an excellent application that let you create engaging exercises in minutes and easily share a varied variety of beautiful and fun activities with your classroom and others.
Commentbox - Commentbox is a jsf component that allows quick realization of a comment functionality
Quizlet - Quizlet allows you to review and create flashcards for a variety of subjects, such as math and reading.