Examples are vending machines, payphones, fire alarms, and information screens in train stations and airports. Such appliances should be designed so that they can be used by anybody, including children, disabled persons, and foreign tourists. Standardization and self-explaining design are important here. If there is a screen with text it may be useful with flags to touch for selecting the language. If faulty operation of a machine has serious consequences then you should pay special attention to the usability.
Examples are medical equipment and dangerous machines.