New Twiddle

components.foo-component\.js

import Component from '@glimmer/component';
import { inject as service } from '@ember/service';

export default class extends Component {
  @service myService;
  
  get bar() {
    console.log(this.myService);
    console.log(this.args.otherThing);
    console.log(this.args.itemComponent);
  }
  
}

components.other-component\.js

import Component from '@glimmer/component';

export default class extends Component {
}

controllers.application\.js

import Controller from '@ember/controller';
import { inject as service } from '@ember/service';
import { action } from '@ember/object';

export default class ApplicationController extends Controller {
  @service myService;
  appName = 'Ember Twiddle';

  @action thingClicked(args) {
    console.log('clicked', args);
  }
}

helpers.my-helper\.js

import Helper from '@ember/component/helper';
import { inject as service } from '@ember/service';

export default class MyHelper extends Helper {
  @service myService;
  
  compute(positional, object) {
    this.myService.things.pushObject(object.item);
  }
}

services.my-service\.js

import Service from '@ember/service';
import { tracked } from '@glimmer/tracking';

export default class MyService extends Service {
   @tracked things = []; 
}

templates.application\.hbs

{{my-helper
  item=(component "other-component" thing="wibble" onClick=(fn this.thingClicked 123))
}}

<p>Things</p>

{{#each this.myService.things as |thing|}}
  {{component thing}}
{{/each}}

templates.components.foo-component\.hbs

{{component @itemComponent}}

{{this.bar}}

templates.components.other-component\.hbs

Some other component {{@thing}}

<button (on "click" @onClick)>
  Click me
</button>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}