So I'm comfortable labeling OER as "openwashing", given the current draconian copyright environment.
In addition to OpenStax and Khan Academy, I can recommend MIT OCW and, if it's legal in your country, downloading textbooks from Library Genesis.
However, surely Gates is correct when he says, "Courses should be created by educators and subject-matter experts, supplemented with professional development, and regularly improved with feedback from the teachers who use them."