The main function of middleware in application architecture is to act as an intermediary layer that facilitates communication and data management between different software applications or services. Middleware enables various systems to interact seamlessly, regardless of their underlying technologies. It provides essential services such as message queuing, transaction management, and API management, enhancing overall application efficiency and scalability. By abstracting complexity, middleware allows developers to focus on business logic and functionality, making it easier to integrate diverse applications in modern software environments.