MOOC: Khan Academy
Courses: 4,020 videos and 350 exercises on math, biology, chemistry, physics, finance and history. Pictured here: Khan Academy's American civics class includes a section on SOPA/PIPA.
Focus: Primarily K-12 education, but the 10-minute topical videos are designed to help anyone who wants to learn about the subject. There is content in at least 16 languages.
Sources for courses: Khan Academy.
Backed by: Donations and at least $12.5 million in grants from The Bill and Melinda Gates Foundation, Google, the O'Sullivan Foundation, the Valhalla Charitable Foundation and private individuals.
Status: Not for profit.
Leadership: President Shantanu Sinha and founder Salman Khan.