There are lots of textbooks (geared towards middle & high school) put together by CK-12 that could possibly provide a free full curriculum for a variety of subjects! They are pretty math and science heavy, but they also have a couple of history books and some SAT Prep!
Here is a list of all of the books that they have for free on Kindle or Kindle Apps, organized by subject (I’ve tried to also organize them by grade level within each subject, so hopefully I got it right): 😉
