The design should be as minimal as possible so as not to be distracting, therefore making the features that are not included in a pro writing app just as important as the ones that are. It should provide the essential tools necessary to make your job of writing easier, but it shouldn’t provide anything extra that could clutter the interface with options or features you don’t want or need. Since the words themselves are the end goal, it’s important that the pro writing app you choose provides you with a distraction-free user interface that inspires creativity.
A good pro writing app should provide an environment that is aesthetically pleasing and makes it easy for you to focus and create, then allows you to export your work to its final destination as quickly (and painlessly) as possible. It’s not something that gives you a ton of formatting options, but rather helps you focus on your words.
The mission of any pro writing app should be to help you produce words that will eventually end up being posted, printed, or published.
You could also define a pro writing app as a “focused writing app,” one that assists you in getting your words out of our head and onto the page.