I have started to look in to Googles Packaged Apps in Chrome, http://developer.chrome.com/apps which seems to be a great technology, but in an early stage.
My quest
I had some conversations with people involved in the packaged apps development and as it is today you cant have access to the file system without prompt our outside of an apps sandbox. But it might come in the future.
But there is a new project called Node-Webkit that is very similar to Chrome packaged apps where you develop your app in Chrome with HTML, js etc where you also can run nodejs in the browser. Using this you can access the file system and many more things.
Check it out here: https://github.com/rogerwang/node-webkit and https://github.com/rogerwang/node-webkit/wiki
Loading and saving files in Node-Webkit is very easy. It looks like this
var gui = require("nw.gui");
var fs = require("fs");
//Save
fs.writeFile('message.txt', 'Hello Node', function (err) {
if (err) throw err;
console.log('It\'s saved!');
});
//Load
fs.readFile('message2.txt', 'utf8', function (err, data) {
if (err) throw err;
console.log(data);
});