Note: Kit.js is currently in very early development and is not ready for use anywhere. If you'd like to contribute, hit me up on Twitter or something.
Kit.js is a JavaScript port of @bdkjones's awesome Kit language.
Kit adds two things to standard HTML: include statements and variables. You can read about how to use it at incident57.com/codekit/help.html#kit. A *.kit file is HTML with special comments. Kit compiles to HTML, so the Kit language is great for building static sites.
The original Kit compiler (as implemented in CodeKit) is open source, and is available at github.com/bdkjones/Kit.
Kit.js is intended to adhere fairly closely to the original implementation of the Kit compiler in CodeKit. As such, it'll follow the design outlined by Bryan Jones. He explains it best, so head there if you have questions about that.
Because Kit is pretty well spec'd out on CodeKit's Kit Language help page, and because I'm pretty happy using Kit as it is now, I don't plan to fold in a ton of features here. If you feel like something's missing from the language, I suggest submitting a feature request over on the original Kit repo.
The Kit Compiler was originally written by Bryan D K Jones in the fall of 2012. Kit.js was written by Calvin Juárez in 2015. Like the original, the code in this repository is released under an MIT license.