A new version of the open source Epub editor Sigil was released earlier this week. You can now use Sigil to edit not just the text and formatting of an epub eBook, but the spine files as well.It also has a number of bug fixes and tweaks.
Sigil is a multi-platform ebook editor which is designed to edit eBooks in epub format. It can accept any number of files as a source (epub, HTML, txt, images). You can edit the source files and save the output as an Epub file.
You now have the option of either letting the app do the work for you, or you can decide to be exacting and edit by hand. This can be very useful when you want to make an epub eBook for a specific purpose.
via Sigil blog