Sigil is a free, open source ebook editor, it is designed to edit books in ePub format. There is another great alternative which also can edit ePub files called Calibre. Sigil is multi-platform editor available for Linux, Windows, and Mac. If you are looking .EPUB editor for editing and creating ebooks in Linux (Ubuntu/Linux Mint), Sigil can help you all with this kind of stuff including html editing of EPUB ebooks, it can edit books in following formats: EPUB, TXT, and HTML, and export these formats to EPUB.
It offers multi-tabbed interface which is easy to navigate and arranged in quite good manner, with various views, including code view, validation of results, book browser, and WYSIWYG view. It has a table of content (TOC) editor, .EPUB validation and a really nice HTML tidy feature.
