http://helios.io/

Helios is an open-source framework that provides essential backend services for iOS apps, from data synchronization and user accounts to push notifications, in-app purchases, and passbook integration. It allows developers to get a client-server app up-and-running in just a few minutes, and seamlessly incorporate functionality as necessary.

Helios is a constellation of mobile backend components—Mix and match to meet the specific needs of your app. Built on the Rack webserver interface, Helios can be easy added into any existing Rails or Sinatra application, or used by itself.