Hemingway started out life as an app that highlighted common errors to help you proofread. A recent update adds a bunch more features that allows you to do all your writing in the app.
The update adds text formatting to the mix. Now, you can bold, add italics, add headline, and create bulleted lists. From there, you can export that text in either HTML or Markdown.
The update also adds the handy ability to import text from Word and then export back into Word when you're done making edits. The update's free for users who purchased the original app (you should find an email with a link to the update) and is still free as a web app version. The full program can be downloaded for Windows or Mac machines and runs for $US9.99.