Although MIT OCW has been operating for more than 15 years, I consider it important to do this post as there are still many people who do not know about its existence.
MIT OpenCourseWare (OCW) is a web-based publication of virtually all MIT course content. OCW is open and available to the world and is a permanent MIT activity.
“The idea is simple: to publish all of our course materials online and make them widely available to everyone.”
Dick K.P. Yue, Professor, MIT School of Engineering.
There is an offer of about 2340 courses with more than 200 million visitors.
Some of the most popular courses:
Go to MIT OCW: