High Quality Content by WIKIPEDIA articles! Skype (pronounced / skaip/) is a software application that allows users to make voice calls over the Internet. Calls to other users of the service and, in some countries, to free-of-charge numbers, are free, while calls to other landlines and mobile phones can be made for a fee. Additional features include instant messaging, file transfer and video conferencing. Skype was written by Estonia-based developers Ahti Heinla, Priit Kasesalu and Jaan Tallinn, who had also originally developed Kazaa. The Skype Group, founded by Swedish-born entrepreneur Niklas Zennström and the Dane Janus Friis, has its headquarters in Luxembourg, with offices in London, Tallinn, Tartu, Stockholm, Prague, and San Jose, California. One of the initial names for the project was "Sky peer-to-peer", which was then abbreviated to "Skyper". However, some of the domain names associated with "Skyper" were already taken. Dropping the final "r" left the current title "Skype", for which domain names were available.