你用什么作为app应用的后台服务？
Ruby on Rails还是PHP？
PHP+Mysql作为Android app的后台：http://www.tutorialspoint.com/android/android_php_mysql.htm
PHP+Mysql作为IOS app的web service后台：
http://www.raywenderlich.com/2941/how-to-write-a-simple-phpmysql-web-service-for-an-ios-app
http://php.about.com/od/learnmysql/fl/Using-MySQL-with-iOS.htm
Ruby on Rails作为app的后台：
https://matteomelani.wordpress.com/2011/10/17/authentication-for-mobile-devices/
http://collectiveidea.com/blog/archives/2013/06/13/building-awesome-rails-apis-part-1/
http://railscasts.com/episodes/350-rest-api-versioning
你也可以用开源的BaaS项目作为后台：
Baasbox：
http://www.baasbox.com/features/
https://github.com/baasbox/baasbox
DreamFactory：
https://www.dreamfactory.com/features
https://github.com/dreamfactorysoftware/dreamfactory
国外有一些专门做BaaS（Backend as a Service）的公司或者项目，可以参考：
http://nordicapis.com/why-you-should-build-apps-with-an-api-backend-baas/
