Khan Academy

Khan academy logo

Khan Academy is a non-profit educational organization created in 2006 by educator Salman "Sal" Khan with the aim of providing a "free, world-class education for anyone, anywhere". The organization produces short lectures in the form of YouTube videos. In addition to micro lectures, the organization's website features practice exercises and tools for educators. All resources are available for free to anyone around the world. The main language of the website is English, but the content is also available in other languages.

Source: https://en.wikipedia.org/wiki/Khan_Academy