- Project Gutenberg: boasting the title of the oldest, if not the largest, online library, Project Gutenberg that offers hundreds of thousands of free e-books for readers to download. Started in the 1970s by Michael Hart, it has grown into a non-profit organization that allows you to access over 30,000 titles whose copyrights have expired and which now belong to public domain.
- ReadPrint: ReadPrint offers you thousands of free books, novels, poems, essays, and works of fiction to choose from. In 2010, they were included in Time Magazine’s list of 50 best websites. It allows you to navigate their library of over 8,000 titles in several different ways, such as a list of Top Authors, and many more.
- ManyBooks: similar to Project Gutenberg in many respects, ManyBooks is a great place for those who find Project Gutenberg’s basic interface a bit off-putting. Manybooks offers a more polished, user-friendly exterior, and a large number of free e-books to choose from. You can also browse the books by cover art, reviews and summaries.
- EPUB: an extremely popular e-book format designed to run on most devices, such as iPad, iPhone, Sony Readers or the Nook. You can also open it on your computer with the use of appropriate software, such as Adobe Digital Editions or EPUBReader extension for Mozilla Firefox.
- PDF: developed by Adobe, it has consistently been one of the most popular formats for years. It is supported by many platforms, and there are a lot of viewers out there that can open it, such Adobe’s own Acrobat Reader, Foxit Reader, Xpdf, among others.
- MOBI: originally conceived as a PalmDOC format extension, it can be opened by MobiPocket Reader, which can be installed on numerous devices. There are some drawbacks of the format, such as tables being displayed differently on some readers, or images remaining the same size if the font size is changed.