Push notification is always a pain when it comes to find the perfect free service. If you are hosting your WordPress website there is no need to subscribe any of those services. With your server you have already what it takes to send push notifications to your subscriber. No third party service involved, just your WordPress server and your application.
In june Nike introduced it’s “Nike+ Fuelband” app for Android. This was actually a great news for the Android community that was waiting for this day to come, but unfortunately this app is only made available to certain versions of Android, and in only five countries