Here’s another provider of free etexts.
“OpenStax College offers students free textbooks that meet scope and sequence requirements for most courses. These are peer-reviewed texts written by professional content developers. Adopt a book today for a turnkey classroom solution or modify it to suit your teaching approach.
Free online and low-cost in print, OpenStax College books are built for today’s student budgets.”
You also have the option of customizing your own version. More info here.