Desk accessory

A desk accessory (DA) in computing is a small transient or auxiliary 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.

Personal information managers

Early personal information managers, such as Norton Desktop and Borland's Sidekick, provided pop-up calculator, alarm, calendar and other functions for single-tasking operating systems like MS-DOS using terminate and stay resident techniques.

Apple Macintosh

Introduced in 1984, as part of the operating system for the Apple Macintosh computer, a Desk Accessory (DA) was a piece of software written as a device driver, conforming to a particular programming model. The purpose of this model was to permit very small helper-type applications to be run concurrently with any other application on the system. This provided a small degree of multitasking on a system that initially did not have any other multitasking ability.