What is exact meaning of "kitchen sink" in programming?

It is an english word which is basically an approach ie, Kitchen Sink is an approach. Its meaning is:

everything that can be conceived of

From [Collins English Dictionary]

The English phrase "Everything but the kitchen sink" means "almost anything one can think of".

Looking at the first 8 Google results for github kitchen sink, it's pretty clear that it's generally used for demo applications which showcase all (or almost all) of the features of an API, generally for use by developers who're learning about the platform. Here are details of the first 5 results:

• Appcelerator kitchen sink: application consisting of multiple stacks of windows... A starting point for tab-based applications
• Reapp kitchen sink: demo app, showing off reapp-ui
• Spotify kitchen sink: demo application for the Spotify Apps API ... designed to help developers who are getting started
• AEM Apps Kitchen Sink: An AEM App which demonstrates the usage of various Cordova/PhoneGap APIs
• Kony Development Cloud KitchenSinkApp: showcases many of the features available to developers