Your Favorite Invention?

Its not really world-affecting, but for a technology class in high school about bioluminescence techniques developed by emmet chapelle, which was very interesting. He tried to get nasa to use his dectectors a sa means for searching for alien life. However, it found more practical use in agriculture and world heath, and it could detect bacteria content in food and water and atp levels in plants to determine their health.

Otherwise, the discovery of antibiotics was very interesting.