I'm generally a fan of SciTE. It runs on Linux, Mac and Window with the exact same UI; you can drive it with a keyboard alone. It is very simple to use, but it'

I'm generally a fan of SciTE. It runs on Linux, Mac and Window with the exact same UI; you can drive it with a keyboard alone. It is very simple to use, but it's intended as an editor for code (it has built-in syntax hiliting for a large number of languages) so it may not be _exactly_ what he is looking for unless he writes his letters in LaTeX...