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

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

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]

It's generally used in very informal contexts for personal repos that have a bit of everything in them. It's a colloquialism so usage varies widely: "miscellaneous" is a more formal term for it.

These are often a collection of utilities handy for the developer, demonstrations, or hobby projects. They may not intended for wider use or release. They may not be structured or documented well as if they had been designed for that. Do not expect them to follow the Unix philosophy of "do one thing well". It is the exact opposite of this approach.

While they can be developed into things that are useful for end users, their main purpose is usually for other developers or the developer themselves to refer back to and avoid "re-inventing the wheel" for tasks that they do often.

miscellaneous

(of items or people gathered or considered together) of various types or from different sources.

(of a collection or group) composed of members or elements of different kinds.