The earliest documented use of the term gadget in context of software engineering was in 1985 by the developers of AmigaOS, the operating system of the Amiga computers (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.