Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
calibre - Ebook manager, viewer & converter
RenPy - Ren'Py is a free and cross-platform visual novel engine that helps you use words, pictures, and...
FBReader - FBReader is an e-book reader for various platforms. Features:
Quest - Quest lets you create sophisticated text-based games, without having to program.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.