Sigil Portable is an ePub ebook editor with support for both WYSIWYG word processor style and direct code editing. It's packaged in PortableApps.com Format so it can easily integrate with the PortableApps.com Platform. And it's open source and completely free.

Sigil is a multi-platform EPUB ebook editor with the following features.
Sigil provides advanced automatic conversion features for all imported documents to the Unicode text encoding.
Sigil also offers a metadata editor with extended support for all types of metadata entries (over 200) that enable you to insert a full description for each.

Features
* Online Sigil User's Guide, and Wiki documentation
* 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 Portable is packaged in a PortableApps.com Installer so it will automatically detect an existing PortableApps.com installation when your drive is plugged in. It supports upgrades by installing right over an existing copy, preserving all settings. And it's in PortableApps.com Format, so it automatically works with the PortableApps.com Platform including the Menu and Backup Utility.

Sigil-0.9.3 Released!
Sigil 0.9.3 is a major new release that greatly improves Sigil’s ability to work with and generate epub3 ebooks without losing any of its epub2 capabilities. This release also includes a number of bug fixes and stability improvements.
- The main bug fixes are:
* Add a python based updatechecker for Sigil updates to prevent Windows OpenSSL build issues
* Stop ‘Generate TOC’ from introducing unnecessary spaces in front of class attibute values
* Use localeAwareCompare to attempt to add Index Entries to build them sorted
* Fix segfault caused by use of possibly stale htmlresource pointer in FlowTab destructor
* Workaround a Qt bug that causes slow selection/highlighting of xhtml in CodeView on Linux
* Fix multiple typos in sigil_gumbo_bs4_adapter code and other plugin interface fixes
- The main new features aavailable for both epub2 and epub3 users are:
* Add an autostart/autoclose capability for plugin developers to simplify the plugin user’s experience
* Add 3 User-assignable ToolBar Buttons for up to 3 plugins – users can now an assign key accelerators to them
* Add General Settings Preference for setting default (epub 2 or 3) for new documents
* Merge CleanSource Preference Settings into General Settings Preferences