Calculus has many applications in fields like engineering, science, economics, and more. It is used to design skyscrapers, bridges, and vehicles as well as model physical phenomena, predict economic trends, and study biological growth and ecosystems. Some examples given include using calculus in robotics, astronomy, space travel, tracking drug concentration in the body, and measuring variables in engineering, science, and business applications. Calculus has become an essential mathematical tool across many domains due to its ability to model changing rates.