There are many interesting posts available in Brain Pickings website about Science, History, Philosophy, Productivity, etc.
1. Brain Pickings
Online courses from popular universities can be accessed from the Coursera e-learning platform.
Using the Mental Flos website, you can test your knowledge with mind testing games and quizzes.
3. Mental Floss
Reddit is a free platform where you can teach anything to anyone and discuss any topic with others.
In Wikipedia, all types of information of the world such as places, popular humans, earth, space, and countless information are available in it.
All these websites can be very helpful for you and you can get knowledge about any topic from them.