[yesenadam]

Books are available free at:

https://archive.org/

https://libgen.rs/

Archive.org tends to have out-of-copyright stuff, LibGen newer stuff, but stuff in between (mid to late 20th C) you can often get by "borrowing" the ebook from archive.org for a short time (free, requires sign-up.) LibGen also has the vast majority of scientific papers/journal articles I look for, no matter how old or obscure.

[dredmorbius]

I'm a fan of the Samizdat sources (you could add ZLibrary as well).

Archive.org's holdings are truly amazing for older works. Newer, in-copyright works can be checked out, though I find the e-reader software, which works well on desktop, is poorly-suited to tablets.

Other sources of legal works include:

- Project Gutenberg: https://gutenberg.org/ (60k books)

- Standard Ebooks: very-well formatted quality ebook, largely public domain https://standardebooks.org/

- Wikisource: https://en.wikisource.org/ Public-domain works, downloadable in ePub and other formats.

There are numerous other smaller collections focusing on specific topics which may also be useful. Searching for "filetype:pdf", "filetype:epub", or "filetype:djvu" may find ebook formats elsewhere.

[wolverine876]

> Archive.org tends to have out-of-copyright stuff

Their lending library has lots and lots of in-copyright stuff. With a free account (takes minutes to setup), you can borrow them (read in an online browser, or via DRM-controlled PDF) for an hour or for two weeks. My impression is that they limit simultaneous borrowers to the number of physical copies the Archive possesses.

If it sounds too good to be true, give it a try. It's only drawback is a poor search engine (just use a general one like DuckDuckGo and add "site:archive.org" to your search)