Glass.

A few points from one of my favorite books:

• Mirrors (played a role in enabling the renaissance, allowed people to see a clear reflection of themselves and reality)
• Telescopes (enabled us to understand the cosmos and earth’s relationship to it)
• Glasses (enabled most Europeans to read once the printing press was discovered)
• Glass fibers (crucial for fiber-optic cables and the internet today)
• Microscopes (enabling humans to study bacteria, and radically improve health standards)
• And then all the obvious use cases like windows, device screens, skyscrapers