In computer software, a widget engine is a software service available to users for running and displaying applets on a graphical user interface, such as that of the desktop.
The term widget engine is not to be confused with that of a widget toolkit. Toolkits are used by GUI programmers, who combine several widgets to form a single application. A widget in a toolkit provides a single, low level interaction, and is prepared to communicate with other widgets in the toolkit. On the other hand, widget engines such as desktop widgets and web widgets are intended for end users. Desktop and web widgets are stand-alone, task-oriented applications which can be composed of several related interactions on its own. Each widget serves only a purpose that is usually addressed by the effort of one GUI widget in a full-scale application.