Multi-platform EPUB ebook editor - Sigil

Sigil is a multi-platform EPUB ebook editor with the following features

 * Online Sigil User's Guide, and Wiki documentation
 * Free and open source software under GPLv3
 * Multi-platform: runs on Windows, Linux and Mac
 * Full UTF-16 support
 * Full EPUB 2 spec support
 * Multiple Views: Book View, Code View and Preview View
 * WYSIWYG editing in Book View
 * Complete control over directly editing EPUB syntax in Code View
 * Table of Contents generator with multi-level heading support
 * Metadata editor with full support for all possible metadata entries (more than 200) with full descriptions for each
 * User interface translated into many languages
 * Spell checking with default and user configurable dictionaries
 * Full Regular Expression (PCRE) support for Find & Replace
 * Supports import of EPUB and HTML files, images, and style sheets,
 * Documents can be validated for EPUB compliance with the integrated FlightCrew EPUB validator
 * Embedded HTML Tidy: all imported files have their formatting corrected, and your editing can be optionally cleaned

Sigil Installation:
Open the terminal and type following command to add the Sigil repository to make sure that Sigil remains updated.

sudo add-apt-repository ppa:rgibert/ebook

Now, type following command to install Sigil

sudo apt-get update
sudo apt-get install sigil

After successful installation, you can open Sigil from the Unity 'Dash'