With over 600 million registered users, Skype is a leader in online video communication and instant messaging. Skype registration is free, and gives users the ability to call, video chat, or instant message peer Skype members at no cost. Skype is compatible with both Mac and PC, and allows file transfers and video conferencing for up to 25 people at a time. For international landline calls, Skype offers credits, monthly memberships at a discounted rate, and a pay as you go option for as low as $0.01/min.