Textbook companies in the US are using various dirty tricks to stop
college students from buying used textbooks and saving money. This
includes corrupting professors with bribes that carry big labels
saying "This is not a bribe."
But it also includes other trickery, such as making textbooks change
in trivial ways from year to year or from school to school. And, of course,
making students subscribe to access to an unjust ebook, which typically has
all the injustices of other commercial ebooks.
When people talk about "open educational resources," or "open"
textbooks that are "free to download," we cannot tell right away
whether they are free/libre or not. That's because the definition of
that term accepts some nonfree licenses.
But I think these "open" textbooks are in fact free/libre. The law
that funds their development requires a license like CC-BY, and they
are developed by an organization called LibreTexts which seems to
recommend only free software tools.
However, cannot verify this. I was unable to find anything on
libretexts.org which spoke about the licensing of their textbooks.
The front page talks about the practical benefits, the things naive
people would appreciate, but says nothing about freedom.
Perhaps there is information present which I could not find. Some of
the home page's navigation does not work without running some nonfree
JS code. I will ask them.