Open Educational Resources

Open educational resources (OER) are freely accessible, openly licensed documents and media that are useful for teaching, learning, and assessing as well as for research purposes. 

OER Commons 

Open 4 the US OER

https://educationaltechnology.net/open-free-educational-resources-oer-teaching-learning/#google_vignette:~:text=The%20list%20includes%3A,%C2%A0%3E%20open%20educational%20resources