Sigil - Sigil is a multi-platform WYSIWYG ebook editor. It is designed to edit books in ePub format.
Vellum - Free beautiful hand-curated wallpapers for the iPhone
calibre - Ebook manager, viewer & converter
Pressbooks - Create books: print and ebooks
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
To EPUB - Instantly convert text documents and ebooks to EPUB format with this free online EPUB converter.