Textbooks
- CK-12 - Free Textbooks - Used to be CC-BY-NC. They now have their own licence which is pretty free but says they can somehow re-appropriate any changes you make, or something.
- Utah open textbooks - K-12
Tertiary (mostly)
- Textbook Equity
- BC Campus - seems to be British Columbia, Canada.
- Open Textbooks: UMN (university of minnesota?)
- Libretexts - physics section
- Portland State University open textbooks
- University of Arkansas OER
- Open Oregon
- Delft University of Technology
- Virginia Tech open textbooks
- Open Stax
- ANU Press - A lot of books from academics, and a lot of them free to download.
- Science books online - points to other sites
- Open Textbook Store - Small range, mostly maths. Looks tertiary.
- Open Culture free textbooks