Introduced In: 10.4 "Tiger" (2005)
To be fair, widgets first came to Mac OS X in 2003 through a program called Konfabulator (now known as Yahoo! Widgets). Two years later, Apple improved on the idea by developing a separate layer of Mac OS X where all the widgets would live.
Akin to mobile apps, widgets are Internet-connected programs that have a simple, focused purpose. When Apple first introduced widgets, developer interest was high, with new widgets dropping everyday. Now with mobile apps being more financially viable market, most of those developers have moved on. As have most of the users. Reportedly, usage has dropped off significantly over the years. But we still find ourselves using it to quickly check the weather or do a quick calculation.