calibre - Ebook manager, viewer & converter
FBReader - FBReader is an e-book reader for various platforms. Features:
Amazon Kindle - Amazon Kindle software lets you read ebooks on your Kindle, iPhone, iPad, PC, Mac, BlackBerry, and...
ibooka - The all-new Apple Books has been redesigned to make finding, reading, and listening to books a beautiful, effortless experience on iPhone and iPad.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.