Boxcar 2 has just been updated to add back a bunch of the features that went missing when the notifications app upgraded from v1.x. Now you can create an account to let you share notifications between devices, configure alerts sounds and more.
Boxcar first got popular back before iOS had proper local notifications for things like email, and stayed that way thanks to integration with third-party services like IFTTT. Used with these services, you can get a notification on your iDevices for virtually anything that happens on the internet and even in your home if you use something like a WeMo switch.
v2.0 looked a lot nicer, and probably got some great changed under the hood, but it was a step back in terms of features.
Now you get those back. You can create an (optional) account to let you sync alerts between devices, you can choose which mail and Twitter clients open when you swipe a notification, you can add an RSS feed to get alerts when it updates – handy for rolling your own news alert service.
In short, Boxcar is back to where it was, only better and much easier to use. And it remains free.