Sigil
Sigil is a multi-platform EPUB ebook editor
Sigil is a free, open-source EPUB editor designed for creating, modifying, and formatting digital books. It supports EPUB 2 and EPUB 3 standards, making it suitable for authors, publishers, and e-book developers. The application provides both visual editing and direct access to XHTML and CSS source code. Users can organize chapters, images, stylesheets, and other publication resources through an integrated file browser.