Features:

• Free and open source software under GPLv3
• Multi-platform: runs on Windows, 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
• Native C++ application
• Bugs :)
• And a lot more...