Hangouts intelligently manages notifications: Once a notification has been read, it will no longer appear on other devices (the software is available on Android and on the web). The chat history and calls is obviously very deep - it is possible to delete a conversation. The application is free and universal.
Essentially , with Hangouts application, Google will make it possible for you with this service to have an alternative to the Apple Facetime and iMessage together integrated into a single app. Using this service will require all obviously a Google account. Application is of course available on Google Play so you can chat with users of Android, to create video conferencing between smartphones and tablets.
