I think lasers are pretty wack when you think about them through this lens. A small, wand-like object in your hand can make light appear from seemingly nowhere. If it’s powerful enough it can set things on fire or blind people. Not to mention larger ones like laser cutters or the LLD, used to destroy missiles midflight. Thats sure to blow some feudal peasant minds
Most of our weaponry.
Communications is huge.
Depending on how far back you go, almost anything. Tech has come a long way and it still seems to have endless possibilities. We just might be in a golden era. We once deemed things impossible and brushed them aside, now we are more accepting of them only being impossible for current tech. Interstellar travel for example is tech that’s still far beyond us but we know we can get there.