A gadget is a small technological object (such as a device or an appliance) that has a particular function, but is often thought of as a novelty. Gadgets are invariably considered to be more unusually or cleverly designed than normal technological objects at the time of their invention. Gadgets are sometimes also referred to as gizmos.
Mechanical gadgets
Clocks, bicycles, and thermometers are amongst the very large number of gadgets that are mechanical and also very popular. The invention of mechanical gadgets though is based more on innovation from the inventor rather than his education

iphone
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Electronic gadgets
Electronic gadgets are based on transistors and integrated circuits. Unlike the mechanical gadgets one needs a source of electric power to use it. The most common electronic gadgets include transistor radio, television, cell phones and th
e quartz watch.

PSP (PlayStation )
Programmable gadgets
Most of the modern gadgets belong to this category.
Application gadgets
Computer programs that provide services without needing an independent application to be launched for each one, but instead run in an environment that manages multiple gadgets. There are several implementations based on existing software development techniques, like JavaScript, form input, and various image formats.
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The earliest documented use of the term gadget in context of software engineering was in 1985 by the developers of AmigaOS, the operating syste
m of the Amiga computers Intuition Amiga|intuition.library and also later gadtools.library'. It denotes what other technological traditions call GUI widget—a control element in graphical user interface. This naming convention remains in continuing use (as of 2008) since then.
It is not known whether other software companies are explicitly drawing on that inspiration when featuring the word in names of their technologies or simply referring to the generic meaning. The word widget is older in this context.
Examples of electronic gadgets
Useful gadgets: Advanced mobile phones eg. iPhone, GPS navigation device
Novelty gadgets: USB toys, toy grade radio control

GPS navigation
olled cars