I had not seen a number of these websites:
hemingwayapp.com: I haven’t downloaded this as a desktop app but it seems pretty helpful.
https://www.online-utility.org/ Lots of tools here.
http://writersdiet.com/ I bet my students will like this interface.
Evans, Harold. Do I Make Myself Clear?: Why Writing Well Matters. (New York, NY: Little, Brown and Company, 2017.)