Udemy is an online learning and teaching marketplace with over 130,000 courses and 35 million students. Learn programming, marketing, data science and more.

Where they're located: San Francisco, California, USA
Website traffic: 110M/month

4. Coursera

Join Coursera for free and learn online. Build skills with courses from top universities like Yale, Michigan, Stanford, and leading companies like Google and IBM. Advance your career with degrees, certificates, Specializations, & MOOCs in data science, computer science, business, and dozens of other topics.

Where they're located: Jacksonville, Florida, USA
Website traffic: 51.6M/month

5. edX

Access 2000 free online courses from 140 leading institutions worldwide. Gain new skills and earn a certificate of completion. Join today.

Where they're located: Boston, Massachusetts, USA
Website traffic: 17.8M/month