Open Educational Resources (OER), like ebooks and lesson plans, are teaching, learning and research materials in any medium – digital or otherwise – that reside in the public domain or have been released under an open license that permits:
The LibreTexts mission is to unite students, faculty and scholars in a cooperative effort to develop an easy-to-use online platform for the construction, customization, and dissemination of open educational resources (OER) to reduce the burdens of unreasonable textbook costs to our students and society.
From Rice University, an open textbook publisher of high-quality print and mobile platform texts for general education courses. Many include supplemental resources.