Sigil 1.9.2

Sigil

Sigil is a free, open source, multi-platform ebook editor. It is designed to edit books in ePub format (both ePub 2 and ePub 3). It also provides features for advanced users, like direct XHTML, CSS and XPGT editing. You can use it to add any of the metadata entries supported by the EPUB specification and create a hierarchical Table of Contents.

Sigil key features:

Free and open source software under GPLv3
Multi-platform: runs on Windows, Mac, and Linux (note Linux only receives limited support)
Full UTF-16 support
EPUB 2 spec support with limited EPUB 3 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
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
All imported files have their formatting corrected, and your editing can be optionally cleaned
Plugins!

Sigil 1.9.2 changelog:

fix loss of highlight on match when searching
fix incorrect search counts
fix incomplete replace all
fix useability issues in Saved Searches
fix handling or subcapture replacements when no search capture groups are provided
fix crash on Windows from too fast/repeated Find Net and Find Previous launched via keyboard shortcuts