Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
calibre - Ebook manager, viewer & converter
Apple Books - The all-new Apple Books has been redesigned to make finding, reading, and listening to books a beautiful, effortless experience on iPhone and iPad.
Amazon Kindle - Amazon Kindle software lets you read ebooks on your Kindle, iPhone, iPad, PC, Mac, BlackBerry, and...
ReadOut - ReadOut is a text to speech conversion app by Flying Phoenix that offers features to enable you to import text from a variety of different sources to convert it into speech in various languages right on your mobile phone.
Project Gutenberg - Project Gutenberg offers free ebooks to download.