diff --git a/framework/YiiBase.php b/framework/YiiBase.php
index fb2967a..c32cc28 100644
--- a/framework/YiiBase.php
+++ b/framework/YiiBase.php
@@ -198,6 +198,32 @@ class YiiBase
 	}
 
 	/**
+	 * Returns the root alias part of a given alias.
+	 * A root alias is an alias that has been registered via [[setAlias()]] previously.
+	 * If a given alias matches multiple root aliases, the longest one will be returned.
+	 * @param string $alias the alias
+	 * @return string|boolean the root alias, or false if no root alias is found
+	 */
+	public static function getRootAlias($alias)
+	{
+		$pos = strpos($alias, '/');
+		$root = $pos === false ? $alias : substr($alias, 0, $pos);
+
+		if (isset(self::$aliases[$root])) {
+			if (is_string(self::$aliases[$root])) {
+				return $root;
+			} else {
+				foreach (self::$aliases[$root] as $name => $path) {
+					if (strpos($alias . '/', $name . '/') === 0) {
+						return $name;
+					}
+				}
+			}
+		}
+		return false;
+	}
+
+	/**
 	 * Registers a path alias.
 	 *
 	 * A path alias is a short name representing a long path (a file path, a URL, etc.)
@@ -222,13 +248,13 @@ class YiiBase
 	 * - a path alias (e.g. `@yii/base`). In this case, the path alias will be converted into the
 	 *   actual path first by calling [[getAlias()]].
 	 *
-	 * @throws InvalidParamException the alias does not start with '@', or if $path is an invalid alias.
+	 * @throws InvalidParamException if $path is an invalid alias.
 	 * @see getAlias
 	 */
 	public static function setAlias($alias, $path)
 	{
 		if (strncmp($alias, '@', 1)) {
-			throw new InvalidParamException('The alias must start with the "@" character.');
+			$alias = '@' . $alias;
 		}
 		$pos = strpos($alias, '/');
 		$root = $pos === false ? $alias : substr($alias, 0, $pos);
diff --git a/framework/base/Application.php b/framework/base/Application.php
index b9f01d7..fd6527f 100644
--- a/framework/base/Application.php
+++ b/framework/base/Application.php
@@ -56,6 +56,11 @@ class Application extends Module
 	 * If this is false, layout will be disabled.
 	 */
 	public $layout = 'main';
+	/**
+	 * @var array list of installed extensions. The array keys are the extension names, and the array
+	 * values are the corresponding extension root source directories or path aliases.
+	 */
+	public $extensions = array();
 
 	private $_ended = false;
 
@@ -81,12 +86,19 @@ class Application extends Module
 
 		if (isset($config['basePath'])) {
 			$this->setBasePath($config['basePath']);
+			Yii::setAlias('@app', $this->getBasePath());
 			unset($config['basePath']);
-			Yii::$aliases['@app'] = $this->getBasePath();
 		} else {
 			throw new InvalidConfigException('The "basePath" configuration is required.');
 		}
 
+		if (isset($config['extensions'])) {
+			foreach ($config['extensions'] as $name => $path) {
+				Yii::setAlias("@$name", $path);
+			}
+			unset($config['extensions']);
+		}
+
 		$this->registerErrorHandlers();
 		$this->registerCoreComponents();
 
@@ -206,7 +218,7 @@ class Application extends Module
 	 */
 	public function getVendorPath()
 	{
-		if ($this->_vendorPath !== null) {
+		if ($this->_vendorPath === null) {
 			$this->setVendorPath($this->getBasePath() . DIRECTORY_SEPARATOR . 'vendor');
 		}
 		return $this->_vendorPath;
diff --git a/framework/base/ViewContent.php b/framework/base/ViewContent.php
index 797dba2..8b4e835 100644
--- a/framework/base/ViewContent.php
+++ b/framework/base/ViewContent.php
@@ -28,6 +28,7 @@ class ViewContent extends Component
 	 * @var \yii\web\AssetManager
 	 */
 	public $assetManager;
+
 	public $assetBundles;
 	public $title;
 	public $metaTags;
@@ -45,7 +46,7 @@ class ViewContent extends Component
 	{
 		parent::init();
 		if ($this->assetManager === null) {
-			$this->assetManager = Yii::$app->getAssetManager();
+			$this->assetManager = Yii::$app->getAssets();
 		}
 	}
 
diff --git a/framework/web/Application.php b/framework/web/Application.php
index f9b615d..32f6479 100644
--- a/framework/web/Application.php
+++ b/framework/web/Application.php
@@ -98,6 +98,15 @@ class Application extends \yii\base\Application
 	}
 
 	/**
+	 * Returns the asset manager.
+	 * @return AssetManager the asset manager component
+	 */
+	public function getAssets()
+	{
+		return $this->getComponent('user');
+	}
+
+	/**
 	 * Registers the core application components.
 	 * @see setComponents
 	 */
@@ -117,6 +126,9 @@ class Application extends \yii\base\Application
 			'user' => array(
 				'class' => 'yii\web\User',
 			),
+			'assets' => array(
+				'class' => 'yii\web\AssetManager',
+			),
 		));
 	}
 }
diff --git a/framework/web/AssetManager.php b/framework/web/AssetManager.php
index 6c32687..1f82e7c 100644
--- a/framework/web/AssetManager.php
+++ b/framework/web/AssetManager.php
@@ -91,7 +91,13 @@ class AssetManager extends Component
 		} else {
 			$this->base = realpath($this->basePath);
 		}
-		$this->baseUrl = rtrim(Yii::getAlias($this->getBaseUrl), '/');
+		$this->baseUrl = rtrim(Yii::getAlias($this->baseUrl), '/');
+
+		foreach (require(YII_PATH . '/assets.php') as $name => $bundle) {
+			if (!isset($this->bundles[$name])) {
+				$this->bundles[$name] = $bundle;
+			}
+		}
 	}
 
 	/**
@@ -103,11 +109,18 @@ class AssetManager extends Component
 	public function getBundle($name, $publish = true)
 	{
 		if (!isset($this->bundles[$name])) {
-			$manifest = Yii::getAlias("@{$name}/assets.php", false);
-			if ($manifest === false) {
+			$rootAlias = Yii::getRootAlias("@$name");
+			if ($rootAlias !== false) {
+				$manifest = Yii::getAlias("$rootAlias/assets.php", false);
+				if ($manifest !== false && is_file($manifest)) {
+					foreach (require($manifest) as $bn => $config) {
+						$this->bundles[$bn] = $config;
+					}
+				}
+			}
+			if (!isset($this->bundles[$name])) {
 				throw new InvalidParamException("Unable to find the asset bundle: $name");
 			}
-			$this->bundles[$name] = require($manifest);
 		}
 		if (is_array($this->bundles[$name])) {
 			$config = $this->bundles[$name];
@@ -116,7 +129,11 @@ class AssetManager extends Component
 				$this->bundles[$name] = Yii::createObject($config);
 			}
 		}
-		// todo: publish bundle
+
+		if ($publish) {
+
+		}
+
 		return $this->bundles[$name];
 	}