• 20 best websites to download free E-books
   
• American Memory

  This Library of Congress site offers "free and open access through the Internet to written and spoken words, sound recordings, still and moving images, prints, maps, and sheet music that document the American experience."
   
• Barnes & Noble Free E-books

  Barnes and Noble offers free e-books, including some popular fiction titles, self published e-books, and classic fiction titles. (Can be read with any of these devices or apps.)
   
• DailyLit

  DailyLit sends you installments of free books so that you can read in shorter amounts.
   
• Digital Public Library of America

  The DPLA contains descriptions of "millions of photographs, manuscripts, books, sounds, moving images, and more from libraries, archives, and museums around the U.S. Each record links to the original object on the content provider’s website." The copyright statuses vary, so check "Rights" field or look at the provider’s website for more information.
   
• E-Book Directory

  The E-book Directory is an aggregator for links to different online sites which offer free e-books.
   
• Feedbooks
  A Paris-based book seller and distributor of free e-books.
   
• Free E-Books.net

  For fiction e-books, from romance to mystery, or non-fiction, from business information to self-improvement.
  Free E-books.net includes self-published material and non-copyrighted e-books.
   

• Hathi Trust Digital Library

  Many institutions, including JHU, are collaborating to make e-books available to everyone. Once you do something, you'll see LOGIN on the top right (which is free). Logging in will allow you to get more full text.
   
• International Children's Digital Library

  More than 4,000 free e-books for children, in 55 different languages.
   
• Internet Archive

  More than 5 million books and other items from more than 900 content providers.
   

• ManyBooks.net
   
• NASA E-books

  Books about aeronautics, history, and more.
   
• National Academies Press

  Hundreds of academic publications free to read online. Create a free account first. Read more about it at: http://blogs.library.jhu.edu/wordpress/?p=10728|
   
• NCBI (National Center for Biotechnology Info) Bookshelf

  Books about science and healthcare. Here is the FAQ for more information: http://www.ncbi.nlm.nih.gov/books/NBK45610/ .
   
• Online Books Page

  More than 1 million e-books, managed by the University of Pennsylvania.
   
• Open Library

  More than 1,000,000 free e-book titles available. The newer, still in copyright e-books can be lent and there are about 200,000 of those.
   
• Project Gutenberg

  Over 33,000 free e-books are available for download at Project Gutenberg. These are e-books published before the 20th century and are free because their U.S. copyrights have expired.
   
• SmashWords
• This site has quickly become one of the preferred places for self-published authors. This is the list of free books, but there are also books for various low prices, and you can filter by length!
   
• Smithsonian Digital Library

  Here are online books and a few serials from the Smithsonian. They will work on all e-readers.
   
• U.S. Government Printing Office (GPO) e-books

  You can put keywords in the search box, or see the entire list of available books at http://tinyurl.com/ov2tkqu . Most of them are in PDF, mobi, or EPUB.

This list is arranged alphabetically by language.

BELARUSIAN

• Belarusian e-Library: http://knihi.com Literature in Belarusian, with some English, German, and other languages. 

CHINESE

• Classical Chinese Literature: http://zhongwen.com/gudian.htm "This site contains Chinese classics with each character hyperlinked to its definition and etymology." No special software is necessary because the characters are displayed as images. Most works have links to English translations.
• New Threads Chinese Cultural Society: http://www.xys.org Electronic library archive of Chinese classic texts.

FRENCH

• Athena Texts Francais: http://un2sg4.unige.ch/athena/ About 10,000 e-books by French and Swiss authors in literature, philosophy, history, economics, and science, among other topics.
• Bibliothèque nationale de France (National Library of France): http://gallica.bnf.fr More than 2,500 digitized works.

GERMAN

• ngiyaw eBooks: German works with some classic English and Hungarian books also. Formats include: .pdf, .prc, .lit, .tr), and HTML.

MORE THAN ONE LANGUAGE

• Europeana: Access to millions of digitized items from European museums, libraries, and archives.
  Search for the author or title of a book, and on the left side, narrow results by file type (“text”) and by copyright (“public domain marked”).
• Projecti Lonnrot: Finnish and Swedish.

POLISH

• Wolne: Over 2,300 titles available, which you can read online or download in epub, mobi, or PDF.

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Most of this list of free international e-books is courtesy of  Dr. Cavanaugh's Educational Technology website and eBookFriendly.