socrative
Socrative is an online tool that allows instructors to create effective quizzes and other assessments in order to quickly check their students' understanding and provide feedback right away. It's great for engaging students while also doing formative assessment of their understanding. Socrative is browser-based (no downloads are needed) and works with mac and pc computers, tablets, and mobile phones.
To get started:
Learn more about how to use Socrative in class (video | Text)