EPUB is the same format used by the popular Stanza [free, iTunes link] app for iPhone and iPod touch. It's a free and open standard format created by the International Digital Publishing Forum (IDPF), and it's designed for reflowable content that can be optimized to whatever device is being used to read a book file. The IDPF has championed EPUB as a single format that can be used by publishers and conversion houses, as well as for distribution and sale of electronic books.
The format is meant to function as a single format that publishers and conversion houses can use in-house, as well as for distribution and sale. It supports digital rights management, something that's sure to warm the cockles of the hearts of publishers, but there's no DRM scheme that is currently specified as part of the format.
Other ebook readers that currently use the format include the Barnes & Noble Nook, the Sony Reader, iRex Digital Reader, and the iRiver Story.
If you're a budding publisher and want to get your ebook into the iBookstore, you'll need a tool to help you create your document in the EPUB format. Of course, we don't know if just anyone will be able to self-publish for the iBookstore, but Apple does note that they will have books from both "major and independent" publishers available.
For Mac users, the choice of tools is small, but good. First, there's the free Calibre ebook management tool. Calibre converts a number of different file formats to EPUB, so it's a good tool for doing an initial conversion. However, to do a lot of formatting, you'll need a full-powered EPUB editor like Sigil. Sigil is a free open-source editor that runs on a number of platforms including Mac OS X.
Next, there's the inexpensive (US$49.99 for a single license) iStudio Publisher. iStudio Publisher is a full-fledged desktop publishing application that can export text flows in EPUB format -- while that's good to hear, it's unclear if iStudio Publisher EPUB files can include photographs or diagrams.
If you happen to be an Adobe InDesign CS4 (US$699) user, you're in luck. The top-of-the-line tool for design and publishing supports EPUB, and it is possible to create files that will work on Amazon's Kindle as well. Lexcycle, the company that created Stanza, has a complete list of the tools for production and conversion of files here. It wouldn't be surprising to see a future version of Pages develop into a way to create EPUB documents.
While EPUB is a popular format, it's not without criticism. The format is great for text-centric books, but is considered unsuitable for publications that require advanced formatting or detailed layout, such as comic books and technical tomes. That could result in some issues for textbook publishers. The lack of a standard DRM scheme could cause the format to splinter into different factions unless Apple forces the issue by adopting an open scheme.
There are also issues with the lack of detail on links within EPUB books. This makes it impossible or difficult to link ebooks, or even provide links within an EPUB book. It appears from the keynote demonstration that Apple has come up with their own "standard" for linking, as there were very active examples of linking from a table of contents to individual pages within an ebook. The standards for annotating EPUB are also lacking, which means that each company using EPUB is coming up with their own way of handling this.
There's a very good possibility that Apple has created their own in-house standards for DRM, linking, and annotation. If the iPad and iBookstore are the successful products that they can be, Apple could finally force the industry to adopt a more robust EPUB standard.
So, that's it for our roundup of all things EPUB. As TUAW receives more information about how iBook and the iBookstore are going to work, we'll be sure to pass it along.