Any function that relies on change over a domain is reliant on concepts that are fundementally calculus. Control systems, statistical analysis, data science, absolutely everything in networking that doesn't involve calling people on the phone to convince them to give you their password, that is all calculus.

Many things that work with time series data use calculus all the time. Both derivatives and integrals are very useful in that context: derivatives being the rate of change at some particular time step, and integrals being the sum of the changes across a range of time steps.

There's a pretty wide range of applications.