In 2004, Salman Khan started tutoring his cousin over the Internet. In 2006, he began uploading educational videos to YouTube. And in 2009, he quit his day job as a hedge-fund manager to concentrate on Khan Academy, a sort of one-man university. Today the site offers his free lessons in thousands of highly visual 10-minute chunks. Math and science dominate, and students are the primary audience, but Khan is adding additional topics and welcomes adult learners. It's a remarkable undertaking — and with funding from Google and the Bill and Melinda Gates Foundation, it has a bright future.