"Open educational resources (OER) are teaching, learning, and research resources that reside in the public domain or have been released under an intellectual property license that permits their free use and re-purposing by others. Open educational resources include full courses, course materials, modules, textbooks, streaming videos, tests, software, and any other tools, materials, or techniques used to support access to knowledge."
http://www.hewlett.org/programs/education/open-educational-resources
This is a small sampling of the textbooks that are available. More can be found using the "Course Resources" above or OER and Textbook Alternatives: Outside Resources from the HCC Library's OER subject guide.