calibre - Ebook manager, viewer & converter
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.
FBReader - FBReader is an e-book reader for various platforms. Features:
OneNote - Get the OneNote app for free on your tablet, phone, and computer, so you can capture your ideas and to-do lists in one place wherever you are. Or try OneNote with Office for free.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
Standard Notes - A safe place for your notes, thoughts, and life's work