Hemingway used to be a web application. It is now available for both the Mac and Windows. It is supposed to highlights common errors. Use it to catch wordy sentences, adverbs, passive voice, and dull, complicated words." In other words, it does what MS-Word has done for many years.
I have always found these suggestions intrusive and not very helpful. But I am probably in the minority. What I find more compelling is that you can "format with Markdown, preview formatting
side-by-side, and save the HTML." So it's a Markdown editor as well.
It costs $4.99—a lot less than MS-Word.