New Twiddle

components.list-trigger.js

import Ember from 'ember';

export default Ember.Component.extend({
  isActive: Ember.computed('activeItem', function() {
    return this.get('activeItem') === this;
  })
});

components.navigation-header.js

import Ember from 'ember';

export default Ember.Component.extend({
  actions: {
    activateItem(item) {
      if (item.get('isActive')) {
        this.set('activeItem', null);    
      } else {
        this.set('activeItem', item);
      }
    }
  }
});

controllers.application.js

import Ember from 'ember';

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{#navigation-header as |header|}}
  {{#header.trigger as |trigger|}}
    <button onclick={{action header.toggleActive trigger}}>+ {{trigger.isActive}}</button>
  {{/header.trigger}}
  {{#header.trigger as |trigger|}}
  <button onclick={{action header.toggleActive trigger}}>a {{trigger.isActive}}</button>
  {{/header.trigger}}
  {{#header.trigger as |trigger|}}
  <button onclick={{action header.toggleActive trigger}}>b {{trigger.isActive}}</button>
  {{/header.trigger}}
{{/navigation-header}}
<br>
<br>

templates.components.list-trigger.hbs

{{yield this}}

templates.components.navigation-header.hbs

{{yield (hash
  trigger=(component 'list-trigger' activeItem=activeItem)
  toggleActive=(action 'activateItem'))}}

twiddle.json

{
  "version": "0.11.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.2",
    "ember-data": "2.11.0",
    "ember-template-compiler": "2.10.2",
    "ember-testing": "2.10.2"
  },
  "addons": {}
}