Its called Doctopus and here is a quick video of how to use it
By using this app in combination with Socrative, you can really make a huge difference in the way you teach, especially with technology.
By using Socrative, you can get your students to give you there name, and email as a quiz then collect the results in a spreadsheet. This will allow you to then go in Google Docs and use Doctopus. Make sure your students create google accounts using the same email they gave you.