What it's for: Easy creation of e-books.
Why it's great: Creating e-books typically requires wrangling together one variety of command line tool or other. EbookLib provides management tools and APIs to simplify the process. It works with epub version 2 and 3 files, with Kindle support under development.
Provide the images and the text (the latter in HTML format), and you can assemble those pieces into an e-book complete with chapters, nested table of contents entries, images, HTML markup, and so on. Cover, spine, and stylesheet data are all supported, too. A plug-in system allows third parties to extend the library's behaviors.
If you don't need something as full-bodied as EbookLib, there's Mkepub, which provides basic e-book assembly functionality in a library that's only a few kilobytes, but includes features like the ability to add images to a document. One minor drawback of Mkepub is that it requires Jinja2, which in turn requires the MarkupSafe library.