A user interface object built upon the Xt Intrinsics (the X 
Toolkit). Similar to a widget, a gadget lacks certain data 
structures (such as a window) contained in a widget. The gadget 
maintains this data on the client side, rather than on the 
server, as does a widget. Although seldom used with today's 
server performance levels, gadgets remain supported by BX. 

Widget is piece of reusable code that  you can Plug-in to 
virtually any website. Gadget acts just like a widget , 
often fulfilling the same purpose but it is proprietary, it 
only works on a certain websites or a specific set of 
websites.