Z-Library
Most published books that are not too obscure can be found here, usually as EPUB, PDF, or MOBI files. I often use it to look for light novels, literature, reference books, and finished web novels, then read them on my Boox Leaf 2. As a result, I have bought very few books since college; I only buy physical copies of books I think I will reread and want to keep.
Anna’s Archive
Its domain seems to change often, so if it is unavailable, search Google for Anna’s Archive. If you still cannot find it, it is probably keeping a low profile for a while.
Its selection and file formats are much the same as Z-Library’s, though it also seems to include a great deal of academic literature. I have not had much use for that myself. If a book is not on Z-Library, try here.
Kox.moe
A site dedicated entirely to manga.
It appears to redirect between domains and requires registration and sign-in. It supports sending books to Kindle and offers EPUB and MOBI formats, but it does not support reading online.
