Google Play Services 7.5 update shows a glimpse of the functionality that's heading towards Android apps3
Smart Lock for Passwords
This feature retrieves saved credentials from the Chrome Password Manager as part of the login process, and saves new credentials for later use on other Android devices and instances of Chrome. This will let users stay logged in as they move between devices, so they will no longer have to log out or create multiple accounts. Smart Lock supports both traditional passwords and Identity Provider credentials.
Google has added Instance ID, which lets developers retrieve an unique identifier for every app instance. This lets apps authenticate and authorize actions even if they don't have registration and accounts. By looking at the Instance ID token, devs can determine which app instance is sending authorization requests.
App Invites Beta
App Invites is a new piece of functionality for both Android and iOS devices which lets developers invite their contacts to install their preview apps through a standardized user interface. Invites can be sent via SMS and email.
Google Cloud Messaging
GCM gives developers a battery efficient mechanism for sending information to users or beaming upstream messages between a device and a server.
Maps on Android Wear
Developers can now use Maps APIs on Android Wear devices, bringing full-fledged navigation to our wrists, map-based games, and whatever their imaginations can come up with!