Caffeine

Malcolm Gladwell, writing for The New Yorker about caffeine makes one of the kind of facile, reductive cause-and-effect observations that I enjoy but try not to take too seriously.

It is worth noting, as well, that in the original coffeehouses nearly everyone smoked, and nicotine also has a distinctive physiological effect. It moderates mood and extends attention, and, more important, it doubles the rate of caffeine metabolism: it allows you to drink twice as much coffee as you could otherwise. In other words, the original coffeehouse was a place where men of all types could sit all day; the tobacco they smoked made it possible to drink coffee all day; and the coffee they drank inspired them to talk all day. Out of this came the Enlightenment.

Not sure I'd go that far, but caffeine certainly does count as one of the key technologies of modernity.