A single global with a namespace method

namespace.js

//BSD Licensed

var YourGlobal = {
    namespace: function(ns){
        var parts = ns.split("."),
            object = this,
            i, len;
        
        for (i=0, len=parts.length; i < len; i++) {
            if (!object[parts[i]]) {
                object[parts[i]] = {};
            }
            object = object[parts[i]];
        }
        
        return object;
    }
};

//usage
YourGlobal.namespace("foo.bar");
YourGlobal.foo.bar.message = "Hello world!";

YourGlobal.namespace("foo").baz = true;

@nzakas I would also say that namespaces like that one are "old school" now, and using modules e.g. NodeJS style is much more worth it.
I switched to that about half year ago and don't look back.

However I wouldn't point AMD as right solution, AMD concept is ok, where you think of module as of functionality, so one module is already a quite large codebase. On programming level modules are much more fine grain and loading tens (many times hundreds) of such modules with AMD is total overkill.
I write modules Node.js style pack them for browser with modules webmake and then if I need to separate some functionalities (packs of modules) I would use some kind of loader, not sure if AMD, as it seems too big (in terms of API) for such simple needs. If someone is interested I coined better my experiences here: JavaScript Modules

@medikoo - I don't see modules and namespaces as mutually exclusive.

@nzakas they're not, I was rather referring to style of building one big namespace (of namespaces) in one global variable, with Node.js style modules you can build complex applications and don't use global variables at all, also you don't have to nest namespaces as it's in your example.

@medikoo - I'm not sure why you're making so many assumptions about my intentions. Namespacing is still a useful technique, I just wanted to share this code. Use it however you want, with modules, without modules, with Node.js, with a browser...it really doesn't matter to me. This isn't a debate, it's just sharing some code.

@nzakas I thought you're intention was to show new function that may help with client-side modules organization. I just wanted to shed a light on new techniques that developed recently and will be part of standard in a future (Harmony modules), that's it. If I misunderstood your point, sorry about that.