Sigil is a free, open source, multi-platform e-book editor, designed for editing books in EPUB format.

Full UTF-16 support and full EPUB 2 spec support

Multiple views: code view (complete control over directly editing EPUB syntax), book view (WYSIWYG), and preview view

Table of contents generator, metadata editor, multi-language user interface, spell checking tool, EPUB compliance validator, support for find and replace

Import, organize, and manage EPUB and HTML files, images, style sheets, audio, video, and fonts

Resources

Source code repository

Current packages

Wiki documentation

Online user guide

Sigil's development blog

Help forum at MobileRead

Translations