Khan Academy offers “a personalized learning resource for all ages," partnering with some of the most prestigious institutions to teach their community anything from math, science, history, computer programming, among many other worldly topics. They’re “working to make a free, world-class education available for anyone, anywhere" all while pushing brilliant content marketing campaigns through their various social media outlets to make learning fun. Even Bill Gates thinks the Khan Academy model is something to follow, citing on his blog that Khan Academy’s free SAT prep offering as one of his favorite 2015 news stories. The best part -- you can learn for free on their YouTube page along with millions of other students.