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Just that. Maybe Word in the first place, for the spell checking. But, other than that, just use it as a plain text editor.

I also find it useful to create a new file for each chapter.

You don't need Word for spell checking. For instance, Emacs can use ISpell, ASpell, etc.

And in emacs you can use org mode with export to pdf though latex

Good to know. I'll check if Sublime Text supports spell checking as well :)