plugin.php

<?php 

// register a field 
$kirby->set('field', 'author', 'field/author');

// register blueprints
$kirby->set('blueprint', 'blog', 'blueprints/blog.yml');
$kirby->set('blueprint', 'article', 'blueprints/article.yml');

// register a widget
$kirby->set('widget', 'visits', 'widgets/visits');

// register templates
$kirby->set('template', 'blog', 'templates/blog.php');
$kirby->set('template', 'article', 'templates/article.php');

// register snippets
$kirby->set('snippet', 'pagination', 'snippets/pagination.php');

// register controllers
$kirby->set('controller', 'blog', 'controllers/blog.php');
$kirby->set('controller', 'article', 'controllers/blog.php');

// register Kirbytags
$kirby->set('tag', 'article', [

]);

// register page models
$kirby->set('page::model', 'blog', 'MyPlugin\\Models\\Blog');
$kirby->set('page::model', 'article', 'MyPlugin\\Models\\Article');

// register all kinds of hooks
$kirby->set('hook', 'panel.page.update', function() {

});

// create page methods, pages methods, file methods and files methods
$kirby->set('page::method', 'comments', function() {

});

// set options
$kirby->set('option', 'blog.title', 'My Blog');

Setting routes as well:

$kirby->set('route', [
  'pattern' => 'myroute',
  'action'  => function() {
    // Return a page object or false
  }
]);

Is $kirby->set('controller', 'article', 'controllers/blog.php'); actually working?
With 2.3b2 in a plugin I had to give a full path to the controller file:

$kirby->set('controller', 'something', __DIR__ . DS . 'mycontroller.php');