Heyoffline.js is a simple tool that prevents your users from this kind of frustration. Written in CoffeeScript and compiled into JavaScript, the library can warn your users when their network goes down so that they don't lose anything. Once JavaScript is loaded, it can react to the loss of connection and change the page accordingly.
Zippopotamus is an initiative to crowd-source and aggregate zip code information and make it available to the public. Postal codes not only provide information about a region, they also change a lot, which means keeping track is tough. Zippopotamus wants to help by offering an API which could simplify auto-complete forms and auto-location or city, state or country information look-up.