Learn physics and math using the best multimedia content on the Web, then track and share your progress with classmates, friends and colleagues. Knotebooks enables users to find, customize and create dynamic educational documents for people of all levels of understanding — free! Imagine you're looking at an explanation of black holes and the text is too difficult for you. Well, with Knotebooks, you can simply swap out that description for an easier explanation, a video lecture or even a java applet. Customize your learning at a more granular level to tackle complex topics, better grasp concepts and retain the information you have learned.