One of the major difficulties about creating books for ereaders is that you probably can’t afford to buy a Kindle, a Nook, a Sony, an iPhone and an iPad. You might have one of these, but probably not all. So it’s very nice that Amazon offers Kindle Previewer for Mac and PC.
Kindle Previewer will allow you to open a MOBI file, the Kindle’s file format, and give you a pretty accurate representation of what the book will look like on the Kindle, Kindle DX and even Kindle for iPhone and iPad, down to the Kindle font and the light gray Kindle background.
And be advised that Kindle Previewer is not the same as Kindle for Mac or PC. Kindle for Mac or PC uses a different font and the window, of course, can be resized. You can’t resize an actual Kindle.
An important thing to remember about the Kindle is that it uses the most brain dead ebook format out there. Any tricky HTML formatting, like tables, will be ignored by an actual Kindle or Kindle Previewer, but it is my belief that Kindle for Mac or PC will attempt to display some of these tricks.