Sigil is a free, open-source ebook editor for files in .EPUB format.
If you need an .EPUB editor for creating or editing ebooks, you could do much worse than Sigil. This is a clean, crisp and, most importantly, free application that will allow you to import and edit ebooks in .TXT, .HTML and .EPUB format, and convert them to .EPUB for export.
Even if it is your first time editing ebooks, Sigil won’t give you any problems. The multi-tabbed interface is simply and sensibly arranged, with various views, including code view, book browser, validation results, and, of course, a WYSIWYG view so you know exactly how the end product will look.
At the technical end, Sigil has a number of nice functions that make editing much easier. It has a table of content (TOC) editor, .EPUB validation and a really nice HTML tidy feature. Although there are ebook editors out there with more functions, not all of them are this pleasant to use. If you are happy with a basic range of features for your epub editor, Sigil is the one for you.
Sigil is a GPL epub creator and converter that will let you produce great ebooks in a flash.