I went to one of Mr. Tufte's workshops several months ago, and I do believe he mentioned Overleaf while discussing LaTeX. I must admit I had forgotten about it until just now, so thanks for the reminder. It looks like a fairly slick interface (and a nice solution for what I recall was a relatively painful problem i.e. installing and using LaTeX).
Thanks -- yes, I believe he's used Overleaf in his workshops for the past couple of years (starting back when we were called writeLaTeX). The Tufte handout and book templates are ones we use again and again when we're asked for examples of such layouts, and they're very popular.