Introduction to Computer Science using Python is MITx most popular MOOC. 
Since the start in 2012, it has totally 1.2 million enrollments. John Guttag, the Dugald C. Jackson Professor of Computer Science and Electrical Engineering at MIT explains the success in the following way: “Although on the surface it’s a computer programming course with Python, it’s really not about Python or even programming.” Eric Grimson, the Bernard M. Gordon Professor of Medical Engineering and professor of computer science, that co-developed the first version of the course with Guttag, continues: “This course is designed to help students begin to think like a computer scientist.” In this sense, the course produces a mindset of skills and knowledge that is well-adapted for the digital society. Since it is a MOOC it also has borderless accessibility all around the world to no- or very low cost, depending on if the student wants to have a certificate or not after she has finished the course. Source: MIT News http://news.mit.edu/2018/first-mitx-mooc-reaches-enrollment-milestone-0830