Although the P2P model is based on sharing files with many users with everyone acting as a host, many P2P applications can also be configured to only share files with specific people via direct connections to specific IP addresses. The exact method for doing this will vary from P2P application and is beyond the scope of this site. See Wikipedia for a list of P2P applications:
http://en.wikipedia.org/wiki/Peer-to-peer
Also see:
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