A gadget provides a rectangular area on a traditional ('fixed') portal (as opposed to a composite portal). Each gadget contains a control that a user can interact with. For example, the worklist area of the worker's home page is implemented through a gadget.
Gadgets are defined through activities that apply to the Data-Gadget class. By creating a portal rule (Rule-Portal rule type), a developer determines which gadgets are visible to which groups of users. Using such rules, you can control the appearance, labeling, and location of gadgets on a portal layout.