From Google Chrome extensions:
Google Plus Hangouts for Chome bring conversations to life with photos, emoji, and even group video calls for free. Use Hangouts as you move from tab to tab in Chrome, or even without a Chrome window open. With Google Plus Hangouts for Chome, get notifications just once. After you see an alert, it'll be removed on other devices. Snooze your notifications if you'd prefer to respond later, see what you talked about in the past, including shared photos and your video call history, keep a record of any Hangout for just a short period of time by turning history off, and view collections of photos shared from each of your Hangouts.