Heyoffline.js is warns your users when their network goes down. In order to make sure they don’t lose anything. Heyoffline.js is framework-agnostic. No need for jQuery. It’s written in CoffeeScript, and compiled into JavaScript. Heyoffline.js is released under an MIT License, so do with it what you will.

Requirements: JavaScript Framework
Demo: http://oskarkrawczyk.github.com/heyoffline.js/
License: MIT License