Sigil is a multi-platform WYSIWYG ebook editor. It is designed to edit books
in ePub format. 
* Free and open source software under GPLv3
* Multi-platform: runs on Windows, FreeBSD, Linux and Mac
* Full Unicode support: everything you see in Sigil is in UTF-16
* Full EPUB spec support
* WYSIWYG editing
* Multiple Views: Book View, Code View and Split View
* Metadata editor with full support for all possible metadata entries
(more than 200) with full descriptions for each
* Table Of Contents editor
* Multi-level TOC support
* Book View fully supports the display of any XHTML document possible
under the OPS spec
* SVG support
* Basic XPGT support
* Advanced automatic conversion of all imported documents to Unicode
* Currently imports TXT, HTML and EPUB files; more will be added with time
* Embedded HTML Tidy; all imported documents are thoroughly cleaned;
  changing views cleans the document so no matter how much you screw
  up your code, it will fix it (usually)
* An actually usable user interface

WWW: http://code.google.com/p/sigil/