Skype
Skype is an application Software that provides the users the Service of Video Chat and Voice Call. The Video Chat and the Voice calls are done via the Internet.
The Software is available for Desktop , Tablets and Mobile Phones. For Desktop it runs on Windows , MAC and Linux. The Windows Phone , Android , Blackberry and iOS can also run Skype App.
Skype is Improving it's features day by day and now comes with the service of Instant messaging , sharing of files , conference calls and emoticons. With Skype you can call directly on Mobile Numbers or Landline but you need to have Credit in your Skype Account.
The Creators of Skype were Priit Kasesalu and Jaan Tallinn. It is Written in Delphi, c and C++. Skype was released in August 2003 and after many years in May 2011, it was acquired by Microsoft for $8.5 Billion.
Skype to Skype Calling is free for the users but Skype to Mobile Numbers/Landline is chargeable. Originally, the name of the software was decided as Skyper, derived from "Sky Peer-to-Peer" but the Domain name was already taken So , the company has to drop 'r' from it leading to 'Skype'. 
Skype led to the activation of WorldWide users over a 100 Million per Month. 

YearInternational call market share
20052.9%
20064.4%
20088%
200912%
201013%
201233%
201336%
201440%

The Other Platforms which are Supported with Skype :
  • Nokia N800N810, and N900 , which runs on Maemo.
  • Nokia N9 which runs on MeeGo(lacks with Video Calling).
  • The Portable Playstation Slim and Lite Version.
  • Many Smart TV's also come the the feature of Skype like Samsung Smart TV.

On 8 October 2014 Microsoft made a Statement that in INDIA Skype Calling Feature from 'Skype to Mobile Phone/Landline' Will be Stopped Although, the users can still use 'Skype to Skype' Calling Feature.