The freely licensed software (GNU AGPLv3 or later) shown in this video will enable a user to send an EPUB2 file to a WordPress installation. Users will be able to use WordPress as a publishing front-end, where the underlying software is part of a larger online publishing workflow (can be executed on a computer locally, too). With WordPress, lots of freely licensed plugins and themes are available and therefore can be applied onto the text quite easily.

Project: https://publishing-systems.org
Source code (local): https://gitlab.com/publishing-systems/automated_digital_publishing
Source code (server): https://gitlab.com/publishing-systems/automated_digital_publishing_server