@wion @aral How about Focuswriter or Ghostwriter?

I don't use them myself, but I see them recommended fairly often.

Thing is, you really don't need anything fancy if all you want is to compose text. GNU Nano will do the job if you don't want to mess around with vim or emacs.

I prefer the joe editor. Run it with the jstar command, and you get an editor with WordStar-like key bindings.