Peer-to-peer communication software with the capability to make and receive audio and video calls to other Skype clients (for free) and land lines for low cost. Additionally it supports instant messaging, chat rooms, audio & video conferencing, file transfers, text (SMS) messaging and voicemail.
Skype 4.0 introduced a completely overhauled UI. Now by default all Skype conversations take place in the central window. Turning Skype from an small accessory to an app that requires nearly full screen.