A pen, a typewriter, or Tex (although I've not used it in years).
Unfortunately, at work, I'm forced to use Word. I admit, it's quicker for edits and rewrites than working longhand, but I'm really not inclined toward word processors. There's a certain tactile cause-and-effect they lack. I used to use Tex (or one of its variants) in a whole other lifetime, on an IRIX network... I liked it, the keyboards were noisy and clunky and actually felt solid and responsive, and Tex was incredibly versatile.
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"Be uncomfortable; be sand, not oil, in the machinery of this world." - Günter Eich (1907-1972)