The printing press.
That's a good one.
And how about zippers? They were undoubtedly a boon to hygeine - no more peeing in the streets out of desperate need; if a chamber pot or water closet was nearby, you could go do your business in private - and in a hurry!
Refrigeration. It has not only brought comfort to millions, but it's medical applications have saved lives. Also, the benefits of food preservation.
The flushed toilet.
cooking fires
The invention of radial tires has increased safety and wear while decreaing cost over bias ply/recapped tires to such an extent it has to be one of the top inventions in the later quarter of the 20th century.
The wheel
Wonderful replies!! Let's expand the question to include discoveries!
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