Skype is the most popular app for voice and video calling.
In the mobile market, Skype has since long been dethroned by Whats App and Viber, but it still remains the most prominent tool for free communication on computers.
Once you're all setup, you can (almost) instantly connect with family, friends, co-workers, or anyone else who is using the same app.
After you install one of the free video chat apps you see below, there are just a few things you need to make sure you have: an active internet connection, ample bandwidth, a webcam, and an audio input and output device (microphone and speaker).
Like Skype, you can make phone calls to non-oo Voo users (like landlines) if you want to pay a fee.
Otherwise, oo Voo to oo Voo video and audio calls are completely free. For example, oo Voo lets you call a Mac computer from a Windows computer, or an Android phone from an i OS phone.
It supports HD sound quality and (full screen) video that has a quality comparable to DVD.
One neat feature when doing that is that you can see which of your contacts are using Facetime (you can't call someone unless they're also signed up for Facetime).
More » Another similar way to make free HD video calls from your computer is with Nimbuzz.
calls between Skype users are free) and you can make paid audio calls to landlines if you so choose.
More » Google Hangouts is great for many reasons, one being that most everyone can login right away, given that they have a Gmail account.