It contains hundreds of thousands of public domain books that you can read online or download. You can even download the whole collection as a zimfile [2], readable with kiwix [3]. Obviously all without DRM/phone home spywares/forced updates/remote control.

[1] https://en.wikisource.org/wiki/Main_Page

[2] https://wiki.kiwix.org/wiki/Content_in_all_languages

[3] https://www.kiwix.org/en/