A Zone object could be a "subclass" of a Promise. It's something I have considered but I didn't think it'd be necessary for the first release.

> But Promises already provide asynchronous try/catch blocks

They do, if all you use is modules that return promises, and the node ecosystem currently has many modules that don't. For example:

    zone.create(function MyZone() {
      // Within MyZone
      setTimeout(function() {
        // Within MyZone
        throw new Error("Oh noes!");
      });
    }).catch(function(err) {
      // Back in the parent zone.
      // Handle the error here.
    });

The above won't work with promises unless you use a promisified version of setTimeout and return that promise from the constructor function.

Conversely, with zones, chaining callbacks is hard to define conceptually:

    zone.create(function MyZone() {
      // In MyZone
    }).then(function() {
      // Which zone are we in?
    }).then(function() {
      // Which zone are we in?
    });

But if you have a great idea here, bring it on.