Kindle Create is the latest program (2017) to provide Kindle format for eBooks. (KFX) It imports from Word files (doc and docx), allows text editing and limited formatting changes, and exports to KPF files, which can be uploaded to Amazon or converted to other formats in Calibre with a plugin.
Descriptions are from the web site.
If you've prepared a book in Microsoft Word, Kindle Create (Beta) helps you convert it so it's ready to publish to Kindle devices and apps. Kindle Create (Beta) makes it easier to go through the file conversion process, preventing the kinds of errors that can slow down publishing.
Kindle Create (Beta) helps you
- Preview and edit your book as it will appear in Kindle format--before you publish
- Create and edit your table of contents while styling your book.
- Add professionally-designed themes to make your eBook better-looking and easier to read
 Device support
eBooks created using Kindle Create (Beta) can be read on all Kindle devices and apps. Kindle Create (Beta) will output different versions for older devices: devices that don't support enhanced typesetting or Page Flip, in particular. Enhanced Typesetting and Page Flip are available on all Kindle e-readers from the Kindle paperwhite 2 onwards, Kindle Fire Tablets from Kindle Fire HDX 2013 series or newer, and the Kindle reading apps for iOS (iPhone/iPad), Android and PC/Mac Kindle reading Apps.
Kindle Create splits editing into two menus: Elements, like chapter titles and quotations, and Formatting, which has fonts and spacing options. It has three font options: Bookerly (serif), which has replaced Caecilia in newer Kindles, Amazon Ember (sans serif), and Monospace. It also includes the option not to set the font, resulting in the default font for whatever device is used to read. It also allows color, highlighting, line spacing and space between paragraphs (with limited options; the menus have numbers that don't indicate whether they are absolutes or relative to the font size).
It offers pre-set element formatting for many common book elements: Title, chapter titles, subtitles, dedication, first paragraph of chapter (with drop cap), and so on. However, the standard formatting for these can't be changed for a particular project. The text can be edited, but each instance of it in the book will need to be edited separately.
Chapter titles, for example, are always 29-pt sans serif, not bold, centered with a 10-pt indent on each side, and added to the table of contents. While this can be adjusted for each chapter title, there is no way to update all chapter titles at once.
After formatting, the file can be saved, and eventually exported to a KPF file. This is intended only to upload directly to Amazon's CreateSpace system. Because of this, Kindle Create has no metadata functions: Title, author, and ISBN are presumed to be added later, during upload.