Ben Chenowith has just released the inaugural version of his Epub editor.
You can’t use it to edit the text of an Epub, but you can change the metadata. For example, you can set the author, title. or publisher. You can also change the language (this is surprisingly important) or just about any other detail about an Epub eBook (including adding or removing the cover image).
It doesn’t have a name yet, but you are welcome to try it.