"Create public and private rooms and share music, videos, and more, synchronized! Turn your room into a automated TV station, 24/7 radio station, or a simple hangout!"
EdPuzzle is a neat tool that I recently learned about from David Kapuler. EdPuzzle allows you to add your voice and questions to educational videos. On EdPuzzle you can search for educational videos from Khan Academy and Learn Zillion. Once you've found a video you can insert your own voice comments. You can also create a series of questions to go along with your chosen video. Questions are inserted along a timeline that matches the video. That means that your students don't have to wait until the end of a video in order to answer the questions. In that regard the EdPuzzle is similar to Blubbr.tv.
create interactive quizzes that are based on YouTube clips. Your quizzes can be about anything of your choosing. The structure of the quizzes has a viewer watch a short clip then answer a multiple choice question about the clip. Viewers know right away if they chose the correct answer or not.