Skype communication app
Skype is the world's most recognized and first app to make free video calls. It is great to make cheap international calls and can be used to message anyone with a Skype account.
Skype lets you communicate for free with over 250 million users. You will probably find every one of your friends on it. It is great since it is familiar and used by older people like your grandparents.
Skype lets you buy credits and call any phone in the world. This makes it the most used VOIP app out there. Since it was purchased by Microsoft, Skype get some overhaul of the design and features.
One of most useful features is the ability to record any video or voice call from the app. You can do it without the need of an external video recorder. This way you can save and watch important personal or business conversations.
You can learn more about it at Skype's website and follow Skype on Twitter for latest updates.