WhatsApp is a cross-platform messaging application for mobile devices.
Messages sent via the app are all encrypted. An internet connection is needed, either via mobile data or a Wi-Fi signal.
WhatsApp is currently used by over one billion people worldwide, making it most used messaging app.
It runs on pretty much all devices, including Android, BlackBerry, iOS, Symbian, Nokia and Windows, and it is available in several languages.
The application has been written in Erlang.