Amazon released an alternative to the Kindle Create program. It is called the
Kindle Create Add-in for Microsoft Word (Beta).
In my opinion it is a better choice for most uses. It basically tries to standardize formatting in Word documents so that they convert well to e-books.
The big advantage of this for authors is that it just uses standard Word doc/docx files instead of the proprietary format produced by the stand-alone Kindle Create program. This makes it easier to update the book and/or publish it on other platforms.