Emacs is a great platform for many things, and in just a few steps it can be
setup for distraction free writing.
You'll need a copy of darkroom-mode, which can either be downloaded
from the darkroom-mode homepage, or installed using M-x package-install
Once installed it's good to go, but I prefer slightly different
settings to the default.
I use use-package to manage my configuration, but the setup is pretty much the
same without it (just use the contents of the progn expression). The following
will set the font to be larger and will limit the page to 80 columns wide: