iOS: Google updated the Hangouts app today and added a slew of new features. The most notable is the integration with Google Voice, so you can now access SMS and voicemails from your Google Voice account (if you have one) right in the Hangouts app.
Pretty much everything from the Google Voice app is now integrated into the Hangouts app. You can check SMS, voicemail and dial out using your Google Voice account. (Australians can't get their own, but many people have worked around that restriction or set up one for use when in the US.)
Beyond that, the app also gets a way to quickly share your location, add status messages, and a set of sticker packs.
Hangouts (Free) [iTunes App Store]