iOS: Today Google updated the Hangouts app with a couple of useful features that finally adds in proper support for iOS 9.
The big update here is the addition of quick replies from notifications. Now, you can reply directly from the notification itself or from Notification Center. Otherwise, this update does a couple of things to improve notifications all around, including adding in group names and including contact names in the Google Voice notifications.
Hangouts (Free) [iTunes App Store]