Jumping in a little late here but there are a couple of resources that you should check out for high school maths if you haven't already.
This is a foundation focused on OER for math and science curriculum (K-12) but mostly on middle school and higher. They started with open textbooks but have branched out to more online support such as tutoring as well. I know a number of community college faculty that have adapted their open textbooks.
The NROC project has focused on middle school, high school, and community college math. They are a fee-based member consortium but make some of their materials available freely at their hippocampus.org OER repository site. I know several community colleges who are members of their fee-based consortium and happy with those math materials.
Community College Outreach Director, OCWC