"This site has been created to help people learn English language. Adapted books – one of the best and interesting way to increase your vocabulary. Here you can find English ebooks of different levels in epub, mobi, fb2, rtf and txt formats.
Read ebooks on you eBook reader or PC/mac, we are supporting all of them, you only should choose appropriate type, for e.g.: choose mobi for Kindle, fb2/epub for Nook or PocketBook, epub for Nook; you can read on PC/mac books in rtf, or use txt as the simplest format for reading using any device, even on your mobile-phone."
In English e-books you will find adapted readers from elementary to advanced level, and some of which come complete with audio in mp3 format.
The quickest way to find your way round the site is by scrolling down to the bottom of the home page and clicking on the tag Find book, where you will see a comprehensive list of titles classified by author, genre, level, length and audio availability.
H/T to Cristina Cabal.