According to Wikipedia, EPUB (Electronic PUBlication) is a free and open e-book standard by the International Digital Publishing Forum (IDPF). They have the files with the .epub extension.
They are getting very popular nowadays and almost all new and old books are available in electronic format.
Here are some of the best eBook readers. Some of them also support other eBook formats like .mobi too.
1. EPUBReader: EPUBReader is a Firefox addon which enables you to read ePUB files from the browser without any further installation of any software. When ePUB files are download, it will process them and makes ready to read. If you have already obtained the ePUB files, open it from “File -> Open” or CTRL+O or Drag the file and Drop in Firefox.
2. iBooks: It’s one of the built-in apps to iPad and also available in App Store. The downloaded books are available in iCloud so that it’s available in your other iOS enabled devices.
3. FBReader /EPUB Reader: It’s the best and free ePUB Reader for Windows OS. It has easy to use interface. Allows multiple eBooks management and easy scrolling.
4. MagicScroll eBook Reader: It’s a Google Chrome Browser extension to read ePUB Files.
5. Cool Reader: It is an e-book viewer which supports a number of text document formats. Fully customizable palette, text reformatting with any font size, font antialiasing, extra smooth scrolling and a lot of other features turn reading into a pleasure.
6. Mobipocket Reader: It’s one of the popular ePUB eBook readers. It has a lot of features and options but seems inactive in development.
7. FBReader: It is a multi-platform e-book reader. It’s free and supports popular e-book formats like ePUB, fb2, mobi, html, plain text, and a lot of other formats.
8. SumatraPDF: Sumatra PDF is a fast, minimalistic PDFis a PDF, ePUB, MOBI, CHM, XPS, DjVu, CBZ and CBR viewer for Windows with no external dependencies, so you can easily run it from a USB drive.
9. Calibre: It is a free and open source e-book library management application. It is available for Windows, Mac, Linux and also in portable version.
10. Sony Reader: It’s a free eBook reader available for PC, MAC, Android and iOS devices.
11. Adobe Digital Editions: It allows reading and managing eBooks and other digital publications. It’s fast and free.
12. Kindle for PC: It allows reading more than 1 million books. Its whisper sync technology automatically syncs your books across apps. It allows looking up words and managing your books.