Khan Academy

Khan Academy, a nonprofit organization that offers free teaching materials on the Internet to both students and teachers. The Academy of Hanas, created by experts, offers you to learn math, science, and much else.
Personalized learning:
Students learn according to their learning rate, first filling gaps in their knowledge and then accelerating learning.
Teachers complement skills to identify gaps in the understanding of their students and to help their students learn more effectively. 
Founder: Salman Kahn
Established: 2008
Legal structure: non-profit organisation
Headquarters: Mountain View, California, United States
Assets: $60.63 million (2014)
Revenue: $44.82 million (2016)