Zhook is an ebook format that isn’t. To make one:

You create a HTML document, call it index.html.
You mark up the text of the book in this file.
You put all your resources, like images and stylesheets, in the same folder or a subfolder.
You make sure you have a cover.png.
You zip it all up, and change the file extension to .zhook.

The best thing about it is that it’s easily convertible to both ePub and webpage.