Desk Accessory

A desk accessory (DA) is a small helper-type application that can be run concurrently with any other application on the system. Early examples, such as SideKick and Macintosh desk accessories, used special programming models to provide a small degree of multitasking on a system that initially did not have any other multitasking ability.

Read more about Desk Accessory:  Personal Information Managers, Apple Macintosh, GEM, PalmOS