One additional point I didn't get to in my first reply is that with the Nexus you can only transfer small amounts of data through NFC (Near Field Communication). S Beam uses NFC to then open a Wi-Fi Direct link between the Samsung devices and allows the transfer of larger files like songs, pictures, etc. Android Beam can only send smaller files like a website link, contact card (from a phone).
S Beam is a much better tool since it takes the concept of Android Beam and makes it better by allowing the larger files to be transferred.
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