This is just a library (starting as a port of a python library I wrote), which helps me generate epub v3 files. It's not fancy at all, but it does what my programs need it to do.
You can add images and mark them as the cover image. You can generate pages that consist only of a full-page image wrapped in an SVG for scaling. You can add CSS and TOC items.
... and that's about it!
Like I said, it's not fancy.