Skype, now owned by Microsoft, is an incredibly popular instant messaging, voice-over-IP, and video calling service. With Skype you chat with your friends either singularly or in groups, make calls to other Skype users or phones, and make video calls. A peer-to-peer service it still struggles with — or doesn't even try to — sync. Skype's cross-platform support is outstanding, however, with native apps not only for iPhone and iPad but for Mac, Windows, Android, BlackBerry, and more.

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