"Open Educational Resources are teaching and learning materials that you may freely use and reuse, without charge. OERs often have a Creative Commons or GNU license that state specifically how the material may be used, reused, adapted, and shared."
Please explore these selected OER collections. This curated list includes some of well-known Open Educational Resource/Textbook repositories. Please be sure to use a rubric to check the quality of any materials you plan to use for your class.