Skype is a software that lets you make free PC to PC calls to anyone else on Skype, anywhere in the world. And even though the calls are free, they are really excellent quality. If you and your friends, family or business contacts are using webcams, you can also make free video calls. You can even call landlines and mobile phones at really cheap per minute rates (and there's no setup or subscription fee). Skype is available for Windows, Mac and Linux (video calls are currently available only to Windows and Mac users). Free download.http://www.skype.com/