In addition to OpenStax, there are quite a few OER repositories: https://en.wikibooks.org/wiki/Main_Page https://en.wikibooks.org/wiki/Main_Page http://www.coll

In addition to OpenStax, there are quite a few OER repositories: https://en.wikibooks.org/wiki/Main_Page https://en.wikibooks.org/wiki/Main_Page http://www.collegeopentextbooks.org/ http://www.collegeopentextbooks.org/ http://www.ck12.org/ http://www.ck12.org/ http://www.curriki.org/ http://www.curriki.org/ http://beyond.psu.edu/bbookx/ http://beyond.psu.edu/bbookx/ More links to other OER sources: https://www.oercommons.org/ https://www.oercommons.org/ http://www.collegeopentextbooks.org/textbook-listings/textbooks-by-subject/mathematics http://www.collegeopentextbooks.org/textbook-listings/textbo... https://open.umn.edu/opentextbooks/SearchResults.aspx?subjectAreaId=7 https://open.umn.edu/opentextbooks/SearchResults.aspx?subjec... http://campusguides.lib.utah.edu/c.php?g=160393&p=1053364 http://campusguides.lib.utah.edu/c.php?g=160393&p=1053364 I also know of at least a dozen absolutely amazing free textbooks published by the authors, sometimes even with .tex sources available on github. Perhaps it's not a question of availability but of discoverability? Also, it would be nice if teachers could mix content from different sources of OER in order to create custom books.