Sigil

Sigil is an open-source e-book editor for publishing e-books in the EPUB format. Users can take advantage of the WYSIWYG Book View mode to write an e-book exactly how they want the finished product to look or switch to Code View for complete control of the e-book's formatting. Additional features such as find and replace with regular expression support, EPUB compliance validation, spellchecking, and HTML tidy make editing and publishing e-books simple. Sigil also allows you to embed audio and video to bring your e-books to life.