Freenet is a large-scale peer-to-peer network which pools the power
of member computers around the world to create a massive virtual
information store open to anyone to freely publish or view information
of all kinds. Freenet is:

Highly survivable: All internal processes are completely anonymized
and decentralized across the global network, making it virtually
impossible for an attacker to destroy information or take control
of the system.

Private: Freenet makes it extremely difficult for anyone to spy on
the information that you are viewing, publishing, or storing.

Secure: Information stored in Freenet is protected by strong
cryptography against malicious tampering or counterfeiting.

Efficient: Freenet dynamically replicates and relocates information
in response to demand to provide efficient service and minimal
bandwidth usage regardless of load. Significantly, Freenet generally
requires log(n) time to retrieve a piece of information in a network
of size n.

WWW: http://freenet.sourceforge.net/