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Calibre is a free and open source e-book library management application made by users, for users. Many languages, designed around the concept of the logical book, i.e., a single entry in your library that may correspond to actual e-book files in several formats.

FBReader is an e-book reader for various platforms.

Innovative book reader with powerful controls & full functions:

Aldiko is an e-book reader application for the Android operating system. It supports the EPUB industry standard format for digital publications and incorporates facilities for browsing online catalogs on thousands of books (including thousands of free public domain work) and downloading them directly into the users personal library. The application features a bookshelf-like user interface that lets user navigate their collection of eBooks. It also provides a customizable reading experience through configurable font and background color, font size and type, margin size, display brightness, page turn mode, etc. Additionally, the application allows users to import their own books to read them on the go. »

EPUBReader is a Firefox addon which lets you read ePub-files just in the browser. You don't need to install additional software!

A fork of the last GPL version of EBookDroid. Supports the following formats:

With GoodReader on your iPhone, iPod Touch or iPad, you can read virtually anything, anywhere. Books, movies, maps, pictures; GoodReader puts it all in a single app, right in your pocket.

EBookDroid is an open source (GPL'ed) document viewer for Android based on the VuDroid code base.

qAllInOne (aka qAIO) is a free open-source software built using Qt to provide users an All-In-One media player, so it can view images, play videos and audio.

AlReader 2 is an eBook Reader for Windows Mobile and Pocket PC products as well as Windows This is a free program.

Icecream Ebook Reader offers to add EPUB, MOBI, PDF, FB2 books and CBR and CBZ comics to the Library and view them in Table View or Book Shelf modes. It’s easy to find books in the library thanks to filters (you can sort books by categories: All, Recently read, Favorites, and Formats) and search tool. Creation of custom categories in the Library is also supported.

Open Source PDF Viewer for Android based on MuPDF library

Lucidor supports e-books in the EPUB file format, and catalogs in the OPDS format. Lucidor provides functionality to:Read EPUB e-books.Organize a collection of e-books in a local bookcase.Search for and download e-books from the Internet, for example by browsing OPDS catalogs. Convert web feeds into e-books.

eReader Prestigio: Book Reader is a multi lingual, multi format text and audio books reading app. Intuitive interface in over 25 languages and an in app store library with over 50,000 text (for children and adults) books and Text-To-Speech (read along) functionality.