The Free Network Project:

What is Freenet?
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.
History
Freenet is an enhanced Open Source implementation of the system described by Ian Clarke's 1999 paper "A distributed decentralized information storage and retrieval system" (see here). Work started on Freenet shortly after the publication of this paper in July 1999 by Clarke and a small number of volunteers. By March 2000 version 0.1 of Freenet was ready for release. Since March 2000 Freenet has been extensively reported on in the press, albeit primarily due to its implications for copyright rather than for its wider aim, namely freedom of communication.
Freenet development continues at an increasingly breathless pace, releasing a new version almost every two weeks, each with significant performance and ease of use improvements. At the time of writing the 0.4 release, with major architectural, performance, and security improvements, is nearing completion.


Applications
The system provides a flexible and powerful infrastructure capable of supporting a wide range of applications, including:
Uncensorable dissemination of controversial information: Freenet protects freedom of speech by enabling anonymous and uncensorable publication of material ranging from grassroots alternative journalism to banned exposes like Peter (Spycatcher) Wright's and David Shayler's revelations about MI5.
Efficient distribution of high-bandwidth content: Freenet's adaptive caching and mirroring is being used to distribute Debian Linux software updates and to combat the Slashdot effect.
Universal personal publishing: Freenet enables anyone to have a website, without space restrictions or compulsory advertising, even if you don't own a computer.
Freenet is an open, democratic system which cannot be controlled by any one person, not even its creators. It was originally designed by Ian Clarke and is being implemented on the open-source model by a number of volunteers.