iA Writer for Mac and iOS
If writing is on your list of New Year's Resolutions, and you use Apple products, you should check out iA Writer. The app is minimal and easy to use. Powered by iCloud (or Dropbox, if that's your thing), it syncs text quickly and easily between devices. It has full Markdown support, but here's the kicker: it has no preferences.
Instead, iA Writer offers just one font and one type of window configuration. While it does have a Focus mode, full-screen view and a Markdown preview window, when all that's off, the app is just a blank slate for your words. I recently switched to it, and have really come to enjoy the lack of noise and settings. There's nothing in your way with iA Writer.
iA Writer is currently on sale for iOS and the Mac for just $0.99 and $4.99, respectively.