You can now use the app instance to store objects or parameters:

$app = new Application();
$app['twig'] = new \Twig_Environment(...);
$app['debug'] = true;

$app->get('/', function() use ($app) {
    return $app['twig']->load('index.html')->render(array());
});

For sercices, you can even make them lazy loaded and/or shared:

$app['twig'] = $app->asShared(function ()
{
    return \Twig_Environment(...);
});

The challenge is to allow the RouteCollection to be mutable while making
it possible to set Route names. We do not want to set the route name
when creating the Controller (it must be optional, adding it after the
closure is ugly as hell), and RouteCollection does not allow changing
route names after they have been added.

The way to solve this is to add a staging area for these routes. This
staging area is the ControllerCollection. All defined controllers are
added to this area. Once the flush() method is called on the
ControllerContainer, the controllers are frozen (no name change
possible) and added as routes to the RouteContainer.

If you want to make use of the RouteCollection (for example: dumping out
routes to the console), you must explicitly call flush() on the
ControllerCollection. There was no good way to do this implicitly. The
application will also call flush() if you use handle() or run().

TLDR:
a) We can now set route names
b) Call getControllerCollection()->flush() before getRouteCollection()
c) We must document flushing
d) Bulat is awesome

bschussek made significant changes to the EventDispatcher implementation
to make it similar to the one Doctrine2 uses.

most significant change in this commit is that returning something from
an error handler will now stop propagation.

Fixed request not being saved in Framework->request attribute when no matching routes are found for a certaing request URI

the update to the latest Symfony2 replaces Response::setRedirect with a new RedirectResponse class. it also changed some internals of the HttpKernel.