It debuted in System 7.5,[1] but disappeared in Mac OS 8, when the feature was implemented as a part of the Appearance Manager.
A widget was added to the title bar in addition to the double-click method of collapsing a window.
However, several third-party utilities, such as WindowShade X for Unsanity's Application Enhancer software, have brought the ability back to Mac OS.
It has since reappeared as a commercial haxie (an unofficial modification to system software) and offers other features, like translucent windows and minimize-in-place.
The WindowShade control panel itself stems from a third-party utility originally written for System 6.0.7 by Rob Johnston.