Skype (/ˈskaɪp/) is an application that specializes in providing video chat and voice calls. Users can also exchange text and video messages, files and images, as well as create conference calls. Skype is available on Microsoft Windows, Mac, or Linux, as well as Android, Blackberry, iOS, and Windows Phone smartphones and tablets. Skype is based on a freemium model. Much of the service is free, but users require Skype Credit or a subscription to call landline or mobile numbers.
Source: Information extracted from Wikipedia in Oct 2015.