Yahoo! Widgets is a free application platform for Mac OS X and Microsoft Windows. The software was previously called Konfabulator, but after being acquired by computer services company Yahoo! it was rebranded. The name Konfabulator was subsequently reinstated as the name of the underlying rendering engine. The engine uses a JavaScript runtime environment combined with an XML interpreter to run small applications referred to as Widgets, and hence is part of a class of software applications called widget engines.

Note the uppercase "W" in Widget; this is the proper use of capitalization when referring to the actual applets that Yahoo! Widget Engine runs. The aforementioned use of capitalization is unique to this particular widget engine.