diff --git a/docs/guide/basics.md b/docs/guide/basics.md
index f8fddfa..605a023 100644
--- a/docs/guide/basics.md
+++ b/docs/guide/basics.md
@@ -114,9 +114,11 @@ There are several classes provided by framework:
 - FileHelper
 - Html
 - HtmlPurifier
+- Image
 - Inflector
 - Json
 - Markdown
 - Security
 - StringHelper
+- Url
 - VarDumper
diff --git a/docs/guide/url.md b/docs/guide/url.md
index 5c1e990..a3058b5 100644
--- a/docs/guide/url.md
+++ b/docs/guide/url.md
@@ -19,7 +19,7 @@ Creating URLs
 -------------
 
 The most important rule for creating URLs in your site is to always do so using the URL manager. The URL manager is a built-in application component named `urlManager`. This component is accessible from both web and console applications via
-`\Yii::$app->urlManager`. The component makes availabe the two following URL creation methods:
+`\Yii::$app->urlManager`. The component makes available the two following URL creation methods:
 
 - `createUrl($params)`
 - `createAbsoluteUrl($params, $schema = null)`
diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 0081c90..7cb5f7c 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -148,6 +148,7 @@ Yii Framework 2 Change Log
 - Enh #2729: Added `FilterValidator::skipOnArray` so that filters like `trim` will not fail for array inputs (qiangxue)
 - Enh #2735: Added support for `DateTimeInterface` in `Formatter` (ivokund)
 - Enh #2756: Added support for injecting custom `isEmpty` check for all validators (qiangxue)
+- Enh #2775: Added `yii\base\Application::bootstrap` to support running bootstrap classes when starting an application (qiangxue)
 - Enh: Added support for using arrays as option values for console commands (qiangxue)
 - Enh: Added `favicon.ico` and `robots.txt` to default application templates (samdark)
 - Enh: Added `Widget::autoIdPrefix` to support prefixing automatically generated widget IDs (qiangxue)
@@ -243,6 +244,7 @@ Yii Framework 2 Change Log
 	- Renamed `yii\web\User::returnUrlVar` to `returnUrlParam`
 - Chg: Added `View::viewFile` and removed `ViewEvent::viewFile` (qiangxue)
 - Chg: Changed `Controller::afterAction()`, `Module::afterAction()` and `ActionFilter::afterAction()` to pass `$result` by value instead of reference (qiangxue)
+- Chg: `yii\base\Extension::init()` is renamed to `bootstrap()` (qiangxue)
 - New #66: [Auth client library](https://github.com/yiisoft/yii2-authclient) OpenId, OAuth1, OAuth2 clients (klimov-paul)
 - New #706: Added `yii\widgets\Pjax` and enhanced `GridView` to work with `Pjax` to support AJAX-update (qiangxue)
 - New #1393: [Codeception testing framework integration](https://github.com/yiisoft/yii2-codeception) (Ragazzo)
diff --git a/framework/base/Application.php b/framework/base/Application.php
index f44edef..52df984 100644
--- a/framework/base/Application.php
+++ b/framework/base/Application.php
@@ -133,6 +133,11 @@ abstract class Application extends Module
      */
     public $extensions = [];
     /**
+     * @var array list of bootstrap classes. A bootstrap class must have a public static method named
+     * `bootstrap()`. The method will be called during [[init()]] for every bootstrap class.
+     */
+    public $bootstrap = [];
+    /**
      * @var \Exception the exception that is being handled currently. When this is not null,
      * it means the application is handling some exception and extra care should be taken.
      */
@@ -209,6 +214,10 @@ abstract class Application extends Module
     public function init()
     {
         $this->initExtensions($this->extensions);
+        foreach ($this->bootstrap as $class) {
+            /** @var Extension $class */
+            $class::bootstrap();
+        }
         parent::init();
     }
 
@@ -228,7 +237,7 @@ abstract class Application extends Module
             if (isset($extension['bootstrap'])) {
                 /** @var Extension $class */
                 $class = $extension['bootstrap'];
-                $class::init();
+                $class::bootstrap();
             }
         }
     }
diff --git a/framework/base/Extension.php b/framework/base/Extension.php
index 0cbc0cc..7f73d41 100644
--- a/framework/base/Extension.php
+++ b/framework/base/Extension.php
@@ -11,7 +11,7 @@ namespace yii\base;
  * Extension is the base class that may be extended by individual extensions.
  *
  * Extension serves as the bootstrap class for extensions. When an extension
- * is installed via composer, the [[init()]] method of its Extension class (if any)
+ * is installed via composer, the [[bootstrap()]] method of its Extension class (if any)
  * will be invoked during the application initialization stage.
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
@@ -21,9 +21,9 @@ class Extension
 {
     /**
      * Initializes the extension.
-     * This method is invoked at the end of [[Application::init()]].
+     * This method is invoked at the beginning of [[Application::init()]].
      */
-    public static function init()
+    public static function bootstrap()
     {
     }
 }