What system is used in computer appliances and special-purpose applications, such as an automobile, ATM, or media player and are used for a single purpose?

Embedded Operating system.

Explanation:

An embedded OS is a type of specific operating system That is capable of performing a particular task for a machine or device, not the computer system. The main objective of the embedded operating system is to run the code that lets the device do its job.

In the Embedded operating system, the hardware is designed to be small and light as well as compact. The embedded system is used in computer appliances just like an automobile, ATM, or media player, etc.