Video: Google Hangouts vs Viber

Google Hangouts is a live video chat app. It allows to share your screen, collaboratively draw on a whiteboard, edit Google Docs documents, create broadcasts for the unlimited number of viewers. Splitted into group chat app and videoconferencing app. Secure Google Hangouts alternatives are Signal and Telegram.
Viber is a mobile app that provides free international calls and text messages to other Viber users using 3G or Wi-Fi. Uses your existing contact list - check out which of your phone contacts and friends is already on Viber so that you can call and text them for free.
Face to face in the news:

2017 - Viber introduced secret chats with self-destructing messages - a new advantage over Google Hangouts

Viber for iOS and Android got an update today that brings “Secret Chats” to the service for the first time. Like Snapchat, Facebook, Telegram and many others before it, Viber now enables its users to set a timer for their messages, after which they will self-destruct. The new feature also alerts a user if the person to whom they are talking takes a screenshot — that’s another feature that Snapchat pioneered. Viber appears to be pushing its security credentials in a bit to differentiate itself from the rest. It added end-to-end encryption and hidden chats last year.

2011 - Google adds video chat to Android. Skype already enables video calls between Android and iPhone. Viber keeps calm

Earlier this year, we forecast the active competition between Skype and Google for the mobile video chat market. And the companies justify our expectations. Yesterday Google launched the (wireless) update of Android-smartphones, that adds voice and video chat to mobile Google Talk. At first Nexus S models will be updated, then all other devices running Android 2.3 and higher. Built-in video chat on Android will work via Wi-Fi, 3G, 4G networks, and will allow to call from a smartphone to GMail and back. Recall that the operating system for tablets Android Honeycomb already has in-built video chat. Meanwhile, Skype is already ahead of its competitor - it already offers video chat for Android and iPhone, and even lets you make video calls between these devices.

Google Talk Android
However, for now these features are available not in the Skype's mobile client, but in Qik that was acquired by Skype in the beginning of the year. Qik works on Android 2.1-2.3.3, iPhone, iPad 2 and iPod touch with cameras. In addition to video chat Qik allows to to send video mail and upload videos on Facebook, Twitter and YouTube. But the video mail will be free only until June 1, 2011 After that you'll need to pay for monthly or annual fee.

And while Google and Skype are learning the basics of mobile video calls, Fring for couple of weeks completed testing its multi-user mobile video chat and made it publicly available for iPhone and Android: