Nested route w/ default

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  location: 'none'
});

Router.map(function() {
  this.route('project', function () {
    this.route('description');
    this.route('comments');
  });
});

export default Router;

routes.project.index.js

import Ember from 'ember';

export default Ember.Route.extend({
  renderTemplate() {
    this.render('project/comments', {
      into: 'project'
    });
  }
});

routes.project.js

import Ember from 'ember';

export default Ember.Route.extend({

});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.project.comments.hbs

and I am comments

templates.project.description.hbs

hai I am description

templates.project.hbs

hai i am project
{{outlet}}

twiddle.json

{
  "version": "0.8.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.5.1",
    "ember-data": "2.5.2",
    "ember-template-compiler": "2.5.1"
  }
}