What is the best website that provides top universities books, courses, lectures, and resources for free just like "libretexts"?

You will not find most of the textbooks I needed anywhere, for free.

While some universities will teach from Rice University’s “OpenStax” or similar resources, raealize that most courses are not generic, and you cannot substitute any textbook for any other textbook claiming to cover “the same” material.

You are not going to get a free copy of Halliday and Resnik’s Fundamentals of Physics, or Fowles Analytical Mechanics, or the Berkeley Physics Course volumes 1–5.

Athough, apparently, Feynman’s Lectures on Physics books are now available online, thanks to Caltech.

Personally,I cherish my boxed set.