calibre - Ebook manager, viewer & converter
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
FBReader - FBReader is an e-book reader for various platforms. Features:
Standard Notes - A safe place for your notes, thoughts, and life's work
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.