Over a million free e-books listed, many or most of which are available in common downloadable formats such as EPUB and PDF. An international collection, though note that some books are available only in the USA and for those, a proxy or VPN connection or a friend in the USA would be needed.
Books are listed by title, author and subject, there is an occasional blog, and for those who still think the Americans are a laid-back sort of folk, a list of the books they've banned over the years.
There is also a vast list of external links, covering big repositories of foreign language materials and specialized subjects of all kinds which store hundreds of thousands more titles, at least. This alone would keep you busy for hours, and although some of these links are very old, I picked two at random and they were still active. Which is at least 50% more than I'd expected.
It's a very basic, very efficient site with no graphics except in the blog. Although it looks dull, though, you'd be missing out if you moved on in the search for something more flashy. And unlike some sites of this age and nature, it's updated and in touch with the latest out-of-copyright releases. Very good value.