I came across two other libraries:
* Library Genesis (
http://libgen.io): it has a lot of books in pdf and epub formats, mostly science, research, and education related books. They claim that their repository has ~35TB of materials.
* Sci-Hub (
http://scihub22266oqcxt.onion): the repository of science papers taken from paywalled locations, for example from Elsevier publisher. Elsevier receives all articles from researchers for free, has them peer-reviewed also for free. Elsevier then proceeds to slap its copyright on the articles and then charges like $30/article for access, even though they have never been granted ownership by the actual authors. Sci-Hub is currently being sued by Elsevier, but the lady who runs it is defiant.