Skype for Mac allows you to call your contacts and video chat with them, as well as make phone calls to landlines or cell phones. It's also capable of hosting conference calls and group video calls, and offers an accessible text messaging platform. Overall, this is one of the best and most appealing communication apps for OS X. Skype is a little piece of software that lets you make free 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.