Science and technology are full of applications of seemingly abstract and useless mathematics. Here are a selection. Write to submit@musicoftheprimes.com if you know more and we can add it to the data base:

Prime numbers: the key to Internet cryptography.

Knot theory: the mathematics of understanding knots has become an essential tool in understanding the way DNA folds.

Group theory, the theory of symmetry: when a message is put into a sequence of 0s and 1s, properties of strange symmetries in multi-dimensional space are being used to preserve the data from noise that might change some of these 0s and 1s.