busted.js

var dns = require('dns')
  , namespaces
  ;

function Namespace () {
  // every namespace has a default / "global" context
  this.active = Object.create(null);
  this._stack = [];
  this.id     = null;
}

Namespace.prototype.enter = function (context) {
  this._stack.push(this.active);
  this.active = context;
};

Namespace.prototype.exit = function (context) {
  // Fast path for most exits that are at the top of the stack
  if (this.active === context) {
    this.active = this._stack.pop();
    return;
  }

  // Fast search in the stack using lastIndexOf
  var index = this._stack.lastIndexOf(context);

  this.active = this._stack[index - 1];
  this._stack.length = index - 1;
};

function create(name) {
  var namespace = new Namespace(name);
  namespace.id = process.addAsyncListener(
    function () {
      return namespace.active;
    },
    {
      before : function (context) { namespace.enter(context); },
      after  : function (context) { namespace.exit(context); }
    }
  );

  namespaces[name] = namespace;
  return namespace;
}

namespaces = process.namespaces = Object.create(null);

create("__test");

function postToCollector() {
  dns.lookup('nodejs.org', function (error, address) {
    console.log(address);
  });
}

process.nextTick(postToCollector);