With most new markets comes competition, as is the case with online education. Today, there are four major platforms that produce content specifically for online instruction: Coursera, Udacity, and edX, which provide university-level content, and Khan Academy, which largely targets K-12 education. While they all offer content designed specifically for web-based instruction, they differ slightly in missions, delivery, and focus.
http://tech.mit.edu/V132/N34/education.html
