Anne's Archive is an amazing resource with over 31 million free ebooks online. It is described as the largest truly open library in human history. All their code and data are completely open source, and the way the site is set up pretty much side steps all issues of copyright (they are only sharing download links rather than the books themselves).
The Library Genesis site is even bigger, and the downloads are faster, but it's more complex to use, and the domain names are constantly changing, so the simpler Anne's Archive is a better introduction to the world of eBook libraries for a lot of people. We will do a post about Library Genesis soon but in the meantime here are some current addresses for it:
Anne's Archive has 31,603,758 books, and 99,900,496 papers in the database, all available to download. These include a huge range of health books and many WAPF specific titles.
We have been asked how the site works so here are some basic instructions showing how to download the ebooks:
I was trying to keep things simple for people new to eBooks and tested some other more basic eBook readers such as Ice Cream reader, but I prefer having all the features of Calibre (which is free anyway) - it's slightly more complex at first but it does everything I want.
For reading books on an Android tablet or phone I use the Read Era app which is really good. It's not set up for all the more complex text editing stuff that Calibre can do, but is great for displaying and reading your eBook collections. Although its not designed for PC use, it apparently can be installed on a windows PC - I'm about to try doing that and instructions for installing it on a Widows PC are here