Controllers
SailCMS, being a MVC based CMS, has controllers that implement the AppController contract. But you can also run a controller that is not implementing any contract, but it's not recommended.
You can create a controller using Commander:
sh
php sail create:controller <containerName> <controllerName>
What AppController provides
Every controller than extends the AppController class gets an instance of the Router, Request, Response and Locale classes.
By default, the response property is set to return an html template and sets the mime type to text/html.
It also provides a nifty redirect method if you ever need it.