diff --git a/framework/core/src/Event/AbstractConfigureRoutes.php b/framework/core/src/Event/AbstractConfigureRoutes.php
index 3ce06cf61..5474c40f1 100644
--- a/framework/core/src/Event/AbstractConfigureRoutes.php
+++ b/framework/core/src/Event/AbstractConfigureRoutes.php
@@ -14,6 +14,9 @@ namespace Flarum\Event;
 use Flarum\Http\RouteCollection;
 use Flarum\Http\RouteHandlerFactory;
 
+/**
+ * @deprecated
+ */
 abstract class AbstractConfigureRoutes
 {
     /**
diff --git a/framework/core/src/Event/ConfigureApiRoutes.php b/framework/core/src/Event/ConfigureApiRoutes.php
index 47727c913..1bcadbfb5 100644
--- a/framework/core/src/Event/ConfigureApiRoutes.php
+++ b/framework/core/src/Event/ConfigureApiRoutes.php
@@ -12,9 +12,7 @@
 namespace Flarum\Event;
 
 /**
- * Configure API routes.
- *
- * This event is fired when API routes are being registered.
+ * @deprecated
  */
 class ConfigureApiRoutes extends AbstractConfigureRoutes
 {
diff --git a/framework/core/src/Event/ConfigureForumRoutes.php b/framework/core/src/Event/ConfigureForumRoutes.php
index 934f27a48..cc64464fd 100644
--- a/framework/core/src/Event/ConfigureForumRoutes.php
+++ b/framework/core/src/Event/ConfigureForumRoutes.php
@@ -14,9 +14,7 @@ namespace Flarum\Event;
 use Flarum\Forum\Controller\FrontendController;
 
 /**
- * Configure forum routes.
- *
- * This event is fired when routes for the forum client are being registered.
+ * @deprecated
  */
 class ConfigureForumRoutes extends AbstractConfigureRoutes
 {
diff --git a/framework/core/src/Event/ConfigureLocales.php b/framework/core/src/Event/ConfigureLocales.php
index 11a412537..1fb373155 100644
--- a/framework/core/src/Event/ConfigureLocales.php
+++ b/framework/core/src/Event/ConfigureLocales.php
@@ -15,6 +15,9 @@ use DirectoryIterator;
 use Flarum\Locale\LocaleManager;
 use RuntimeException;
 
+/**
+ * @deprecated
+ */
 class ConfigureLocales
 {
     /**
diff --git a/framework/core/src/Event/ConfigureMiddleware.php b/framework/core/src/Event/ConfigureMiddleware.php
index e602d5532..1581bfdbd 100644
--- a/framework/core/src/Event/ConfigureMiddleware.php
+++ b/framework/core/src/Event/ConfigureMiddleware.php
@@ -13,6 +13,9 @@ namespace Flarum\Event;
 
 use Zend\Stratigility\MiddlewarePipe;
 
+/**
+ * @deprecated
+ */
 class ConfigureMiddleware
 {
     /**
diff --git a/framework/core/src/Extend/Assets.php b/framework/core/src/Extend/Assets.php
new file mode 100644
index 000000000..6fb52dbd7
--- /dev/null
+++ b/framework/core/src/Extend/Assets.php
@@ -0,0 +1,81 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Frontend\Event\Rendering;
+use Illuminate\Contracts\Container\Container;
+use Illuminate\Events\Dispatcher;
+
+class Assets implements Extender
+{
+    protected $appName;
+
+    protected $assets = [];
+    protected $bootstrapper;
+
+    public function __construct($appName)
+    {
+        $this->appName = $appName;
+    }
+
+    public function defaultAssets($baseDir)
+    {
+        $this->asset("$baseDir/js/{$this->appName}/dist/extension.js");
+        $this->asset("$baseDir/less/{$this->appName}/extension.less");
+
+        return $this;
+    }
+
+    public function asset($path)
+    {
+        $this->assets[] = $path;
+
+        return $this;
+    }
+
+    public function bootstrapper($name)
+    {
+        $this->bootstrapper = $name;
+
+        return $this;
+    }
+
+    public function apply(Container $container)
+    {
+        $container->make(Dispatcher::class)->listen(
+            Rendering::class,
+            function (Rendering $event) {
+                if (! $this->matches($event)) {
+                    return;
+                }
+
+                $event->addAssets($this->assets);
+
+                if ($this->bootstrapper) {
+                    $event->addBootstrapper($this->bootstrapper);
+                }
+            }
+        );
+    }
+
+    private function matches(Rendering $event)
+    {
+        switch ($this->appName) {
+            case 'admin':
+                return $event->isAdmin();
+            case 'forum':
+                return $event->isForum();
+            default:
+                return false;
+        }
+    }
+}
diff --git a/framework/core/src/Extend/Compat.php b/framework/core/src/Extend/Compat.php
new file mode 100644
index 000000000..3678f2a84
--- /dev/null
+++ b/framework/core/src/Extend/Compat.php
@@ -0,0 +1,38 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Illuminate\Contracts\Container\Container;
+
+/**
+ * This class is used to wrap old bootstrap.php closures (as used in versions up
+ * to 0.1.0-beta7) in the new Extender format.
+ *
+ * This gives extensions the chance to work with the new API without making any
+ * changes, and have some time to convert to the pure usage of extenders.
+ *
+ * @deprecated
+ */
+class Compat implements Extender
+{
+    protected $callback;
+
+    public function __construct($callback)
+    {
+        $this->callback = $callback;
+    }
+
+    public function apply(Container $container)
+    {
+        $container->call($this->callback);
+    }
+}
diff --git a/framework/core/src/Extend/Extender.php b/framework/core/src/Extend/Extender.php
new file mode 100644
index 000000000..71274391e
--- /dev/null
+++ b/framework/core/src/Extend/Extender.php
@@ -0,0 +1,19 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Illuminate\Contracts\Container\Container;
+
+interface Extender
+{
+    public function apply(Container $container);
+}
diff --git a/framework/core/src/Extend/FormatterConfiguration.php b/framework/core/src/Extend/FormatterConfiguration.php
new file mode 100644
index 000000000..1608a35fd
--- /dev/null
+++ b/framework/core/src/Extend/FormatterConfiguration.php
@@ -0,0 +1,36 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Formatter\Event\Configuring;
+use Illuminate\Contracts\Container\Container;
+use Illuminate\Events\Dispatcher;
+
+class FormatterConfiguration implements Extender
+{
+    protected $callback;
+
+    public function __construct(callable $callback)
+    {
+        $this->callback = $callback;
+    }
+
+    public function apply(Container $container)
+    {
+        $container->make(Dispatcher::class)->listen(
+            Configuring::class,
+            function (Configuring $event) {
+                call_user_func($this->callback, $event->configurator);
+            }
+        );
+    }
+}
diff --git a/framework/core/src/Extend/Locale.php b/framework/core/src/Extend/Locale.php
new file mode 100644
index 000000000..08e126b41
--- /dev/null
+++ b/framework/core/src/Extend/Locale.php
@@ -0,0 +1,75 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use DirectoryIterator;
+use Flarum\Locale\LocaleManager;
+use Illuminate\Contracts\Container\Container;
+use RuntimeException;
+
+class Locale implements Extender
+{
+    protected $directory;
+
+    public function __construct($directory)
+    {
+        $this->directory = $directory;
+    }
+
+    public function apply(Container $container)
+    {
+        $this->loadLanguagePackFrom(
+            $this->directory,
+            $container->make(LocaleManager::class)
+        );
+    }
+
+    private function loadLanguagePackFrom($directory, LocaleManager $locales)
+    {
+        $name = $title = basename($directory);
+
+        if (file_exists($manifest = $directory.'/composer.json')) {
+            $json = json_decode(file_get_contents($manifest), true);
+
+            if (empty($json)) {
+                throw new RuntimeException("Error parsing composer.json in $name: ".json_last_error_msg());
+            }
+
+            $locale = array_get($json, 'extra.flarum-locale.code');
+            $title = array_get($json, 'extra.flarum-locale.title', $title);
+        }
+
+        if (! isset($locale)) {
+            throw new RuntimeException("Language pack $name must define \"extra.flarum-locale.code\" in composer.json.");
+        }
+
+        $locales->addLocale($locale, $title);
+
+        if (! is_dir($localeDir = $directory.'/locale')) {
+            throw new RuntimeException("Language pack $name must have a \"locale\" subdirectory.");
+        }
+
+        if (file_exists($file = $localeDir.'/config.js')) {
+            $locales->addJsFile($locale, $file);
+        }
+
+        if (file_exists($file = $localeDir.'/config.css')) {
+            $locales->addCssFile($locale, $file);
+        }
+
+        foreach (new DirectoryIterator($localeDir) as $file) {
+            if ($file->isFile() && in_array($file->getExtension(), ['yml', 'yaml'])) {
+                $locales->addTranslations($locale, $file->getPathname());
+            }
+        }
+    }
+}
diff --git a/framework/core/src/Extend/Route.php b/framework/core/src/Extend/Route.php
new file mode 100644
index 000000000..260bb37a5
--- /dev/null
+++ b/framework/core/src/Extend/Route.php
@@ -0,0 +1,49 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Http\RouteCollection;
+use Flarum\Http\RouteHandlerFactory;
+use Illuminate\Contracts\Container\Container;
+
+class Route implements Extender
+{
+    protected $appName;
+    protected $name;
+    protected $httpMethod;
+    protected $path;
+    protected $handler;
+
+    public function __construct($appName, $name, $httpMethod, $path, $handler)
+    {
+        $this->appName = $appName;
+        $this->name = $name;
+        $this->httpMethod = $httpMethod;
+        $this->path = $path;
+        $this->handler = $handler;
+    }
+
+    public function apply(Container $container)
+    {
+        /** @var RouteCollection $routes */
+        $collection = $container->make("flarum.{$this->appName}.routes");
+
+        /** @var RouteHandlerFactory $factory */
+        $factory = $container->make(RouteHandlerFactory::class);
+
+        $collection->{$this->httpMethod}(
+            $this->path,
+            $this->name,
+            $factory->toController($this->handler)
+        );
+    }
+}
diff --git a/framework/core/src/Extension/Extension.php b/framework/core/src/Extension/Extension.php
index 1abb6febe..255a7c6df 100644
--- a/framework/core/src/Extension/Extension.php
+++ b/framework/core/src/Extension/Extension.php
@@ -231,6 +231,11 @@ class Extension implements Arrayable
         return $this->path;
     }
 
+    public function getBootstrapperPath()
+    {
+        return "{$this->path}/bootstrap.php";
+    }
+
     /**
      * Tests whether the extension has assets.
      *
diff --git a/framework/core/src/Extension/ExtensionManager.php b/framework/core/src/Extension/ExtensionManager.php
index 404638fd5..ad0df4278 100644
--- a/framework/core/src/Extension/ExtensionManager.php
+++ b/framework/core/src/Extension/ExtensionManager.php
@@ -12,6 +12,7 @@
 namespace Flarum\Extension;
 
 use Flarum\Database\Migrator;
+use Flarum\Extend\Compat;
 use Flarum\Extension\Event\Disabled;
 use Flarum\Extension\Event\Disabling;
 use Flarum\Extension\Event\Enabled;
@@ -273,21 +274,30 @@ class ExtensionManager
     }
 
     /**
-     * Loads all bootstrap.php files of the enabled extensions.
+     * Retrieve all extender instances of all enabled extensions.
      *
      * @return Collection
      */
-    public function getEnabledBootstrappers()
+    public function getActiveExtenders()
     {
-        $bootstrappers = new Collection;
+        return $this->getEnabledExtensions()
+            ->flatMap(function (Extension $extension) {
+                $bootstrapper = $extension->getBootstrapperPath();
+                if ($this->filesystem->exists($bootstrapper)) {
+                    $extenders = require $bootstrapper;
 
-        foreach ($this->getEnabledExtensions() as $extension) {
-            if ($this->filesystem->exists($file = $extension->getPath().'/bootstrap.php')) {
-                $bootstrappers->push($file);
-            }
-        }
+                    if (is_array($extenders)) {
+                        return $extenders;
+                    }
 
-        return $bootstrappers;
+                    // Assume that the extension has not yet switched to the new
+                    // bootstrap.php format, and wrap the callback in a Compat
+                    // extender.
+                    return [new Compat($extenders)];
+                } else {
+                    return [];
+                }
+            });
     }
 
     /**
diff --git a/framework/core/src/Extension/ExtensionServiceProvider.php b/framework/core/src/Extension/ExtensionServiceProvider.php
index 77b88d3e5..78b8be201 100644
--- a/framework/core/src/Extension/ExtensionServiceProvider.php
+++ b/framework/core/src/Extension/ExtensionServiceProvider.php
@@ -12,6 +12,7 @@
 namespace Flarum\Extension;
 
 use Flarum\Foundation\AbstractServiceProvider;
+use Illuminate\Contracts\Container\Container;
 
 class ExtensionServiceProvider extends AbstractServiceProvider
 {
@@ -22,13 +23,14 @@ class ExtensionServiceProvider extends AbstractServiceProvider
     {
         $this->app->bind('flarum.extensions', ExtensionManager::class);
 
-        $bootstrappers = $this->app->make('flarum.extensions')->getEnabledBootstrappers();
+        $this->app->booting(function (Container $app) {
+            /** @var \Flarum\Extend\Extender[] $extenders */
+            $extenders = $app->make('flarum.extensions')->getActiveExtenders();
 
-        foreach ($bootstrappers as $file) {
-            $bootstrapper = require $file;
-
-            $this->app->call($bootstrapper);
-        }
+            foreach ($extenders as $extender) {
+                $extender->apply($app);
+            }
+        });
     }
 
     /**