Calligra Words, a KDE word-processing software, will soon support EPUB formats. This support will make it possible for the user to create high quality and portable ebooks compatible with PCs, netbooks, tablets and mobile devices.
Calligra developer Ingwa posted a screenshot of how this feature will possibly look. Below is the EPUB editor in author mode:
For the time being, Calligra doesn't support basic formatting, pictures or chapter splits for EPUB. But hopefully, it will in near future. The developers are currently working on odt-to-epub filter that will make formatting in EPUB possible.