calibre - Ebook manager, viewer & converter
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
FBReader - FBReader is an e-book reader for various platforms. Features:
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .