Anthologize is a free, open-source plugin for WordPress 3.0. It enables WordPress to be used as a platform for publishing electronic texts in PDF, ePUB or TEI format. The plugin enables users to grab their existing blog posts, export content from external feeds or compose new content directly in Anthologize, then apply outlining, create a custom order, and edit content into a single document for export. Anthologize requires a self-hosted or local installation of WordPress.

Sigil is a free, open source, multi-platform e-book editor, designed for editing books in EPUB format.

Full UTF-16 support and full EPUB 2 spec support

Multiple views: code view (complete control over directly editing EPUB syntax), book view (WYSIWYG), and preview view

Table of contents generator, metadata editor, multi-language user interface, spell checking tool, EPUB compliance validator, support for find and replace

Import, organize, and manage EPUB and HTML files, images, style sheets, audio, video, and fonts

Resources

Source code repository

Current packages

Wiki documentation

Online user guide

Sigil's development blog

Help forum at MobileRead

Translations

A simple and easy tool for creating EPUB, MOBI, and other ebook formats.

Calibre is a free and open source ebook library management application, including options for syncing to devices and converting between a large number of formats. Calibre also has a built-in e-book editor for EPUB and AZW3 formats.

Scrivener is software for writing that includes virtual index cards, outlining, version control, import/export options, and scriptwriting features, and provides a management system for notes and documents plus support for document metadata.

It allows the creation of documents from sub documents, ebook (epub and Kindle/mobi) and TeX and LaTeX export as well as ODF, PDF and Microsoft Word exports.

A Linux version is in beta, and an iOS version is reportedly under development