Multi-Platform Client Notification App -- Updated with correct skills (Android, iOS, Windows 8, Mac OSx, and Ubuntu)

I need a set of clients developed. These will be for: Android ICS (and later), Windows 8.x, iOS (6 and later), Mac OSx (10.6.8 and later), and Ubuntu 14.04. Each client has the same functionality. My preference would be for a common solution for the source code, perhaps using Xamarin. But I am open to hearing your ideas. The clients that are will be a part of a larger solution. At a high level, the clients will receive push notifications and display them to the user. For push notification on the mobile devices, we'll be using Google Cloud Messaging and Apple Notification Service. For Mac OSx, Windows and Linux desktop platforms, I would like suggestions for the cleanest push notification solution. In addition to seeing the individual notifications pop up, the user will be able to launch a client app and see previous notifications. (These are retrieved from a web service, which should be checked periodically - set by a parameter). From the notification view, the user will be able to launch another app on the device, based upon information provided in the notification. The other apps will have registered a custom URL scheme. The apps need to support Google, Twitter, Facebook and e-mail authentication. The app will work with a web service to handle the login and also query for information to be presented to the user. The web service will respond with json encoded data, representing a list of elements to display to the user. There are 4 screens to be developed for each platform: 1.) The User Login screen 2.) The individual Push Notification screen 3.) The Notification list screen, showing previous notifications 4.) The Notification detail screen, which allows the user to launch another app on the device. I'll need a simple "hello world" client for each platform that demonstrates it can be launched from the Notification detail screen. I'd like for the client to register a unique URL scheme with the OS, and for the client to use this URL scheme to launch the app. In the attached document, I have quickly described the high level screens to be created and how the interactions are to work. The screens are not exact. I'd like the contractor to create them, using my document as the basic idea. I'll need all source code for each platform along with a short document describing how it compiles and how it works.