RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.
calibre - Ebook manager, viewer & converter
Expresso - The award-winning Expresso editor is equally suitable as a teaching tool for the beginning user of regular expressions or as a full-featured development environment for the experienced programmer with an extensive knowledge of regular expressions.
FBReader - FBReader is an e-book reader for various platforms. Features:
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.