Emacs

Suppose you a text document where you want to wrap every line after 80 characters, but you don't want to break words. Also you want it throughout the whole document, then you can do this:

;; M-: for evaluating a singular expression, can only do one expression each
(set-fill-column 80)
(fill-region (point-min) (point-max))

Of course you can set any document text width, and any specified region.