Socrative

Socrative is a smart student response system that empowers teachers by engaging their classrooms with a series of educational exercises and games. It is simple and take seconds to login. Socrative runs on tablets, smartphones, and laptops. Teachers login through their device and select an activity which controls the flow of questions and games. Students simply login with their device and interact real time with the content. Student responses are visually represented for multiple choice, true/false and short answer questions.

More information: http://www.socrative.com/