Best online(free) courses to study/prepare for AP Tests?

I registered for test only at my school. I have experience with the AP subjects, but would love some extra resources. I know AP has some Daily Videos, but those aren’t really that comprehensive.

If there are good online, free courses to study or prepare for AP Tests, that’d be great!

I think the college board provides some study materials on-line which are free (sample multiple choice questions etc). That being said, the point of the AP class is to cover the material necessary to do well on the test. Neither of my kids really studied separately for the AP exams - they did well in the classes and that seemed enough for them (both got all 4s and 5s).

I have a homeschooled kid who took AP exams after seeing that some of his planned courses (at home or co-op classes) had a syllabus that mostly covered the material on the AP exam. We bought the ‘5 Steps to a 5’ book so that kid could review anything that was confusing and use the books for the practice tests. In the end, the vast majority of review came from watching the College Board’s videos. He found that they gave a good indication of what was going to be on the exam and what the graders were looking for in free response answers. After a bit of trail and error, he found that the best process for him was to start watching videos in the spring semester, starting at the beginning so that it started with review of the first semester’s work. (He ended up with a 4 in Chem freshman year and 5s in Bio, US History, Calc BC, and Engl. Lang, taken 2 each during sophomore and junior years). None of kid’s classes were designed as AP courses so there was no end of year cumulative review or practice test taking in class, so the review and discussion about how to approach the free response questions was really helpful.