Google Hangouts

Use Hangouts to keep in touch. Message friends, start free video or voice calls, and hop on a conversation with one person or a group.
 * Include all your friends with group chats for up to 150 people.
 * Say more with photos, videos, maps, emoji, stickers, and animated GIFs.Turn any conversation into a free group video call with up to 10 friends.
 * Keep in touch with friends across Android, iOS, and the web, and sync chats across all your devices.
 * Message friends anytime, even if they’re offline.
 * Snooze your notifications so you can respond later.
 * See what you chatted about in the past, including shared photos and your video call history.
 * Keep a record of any conversation for just a short period of time by turning history off.
 * Connect your Google Voice account to make calls, send and receive SMS, and access your voicemail.

Hangouts Chrome extension:
 * Use Hangouts and get notifications as you move from tab to tab in Chrome, or even without a Chrome window open.
 * Position Hangouts anywhere on your screen, even if you have more than one monitor. Keep conversations in a single window or pop out the important ones. 
 * View and continue your conversations across devices.
 * Get notifications just once. After you see an alert, it’ll be removed on other devices.

Notes:
 * Unlike the Chat for Google app, Hangouts doesn’t support “invisible status”.
 * Mobile carrier and ISP charges may apply.