New Twiddle

controllers.application.js

import Ember from 'ember';

export default class extends Ember.Controller {
  @controller('other') other

  constructor() {
    super(...arguments);
    this.appName = 'Ember App';
  }
}

controllers.other.js

import Ember from 'ember';

export default Ember.Controller.extend({
  value: 'from other controller'
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<p>
  {{other.value}}
</p>
<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}