A fresh update for Google's chat app Hangouts adds in quick reply functionality. When a notification comes in for a call or message, so will a button that allows you to reply without entering an entirely new window. This is handy if you just want to shoot a quick message to someone, to tell them you're not available for a call or you'll be right back or whatever else.
The other key change in the update is conversation shortcuts, so now you can just click a button on the Home screen to talk to specific people.
You can find the APK at the source.