Konspire
A searchable, distributed file sharing system with no central servers, and resumable file transfers. Written in Java 1.1 for portability.
http://konspire.sourceforge.net/

After Napster - The Beat Goes On
A large listing of Napster alternatives - software for various platforms, search and metasearch services.
http://www.afternapster.com

BadBlue
A free, very small Windows web server for sharing, publishing and serving files.
http://www.badblue.com

StreamSec 2PCube
Integrated client and server with strong encryption designed for small groups on large networks. Features include file sharing, messaging, news and chat.
http://www.streamsec.com/pp2p.asp

Publius Publishing System
Web publishing system that is highly resistant to censorship and provides publishers with a high degree of anonymity.
http://www.cs.nyu.edu/~waldman/publius/

Blubster
Decentralized file sharing system for MP3 files featuring resumable and distributed downloading.
http://www.blubster.com

Endeavors Technology
Provides secure peer-to-peer (P2P) collaboration networks with its product, Magi Enterprise for PCs, laptops and Windows CE handheld devices. Includes messaging, WebDAV publishing and encryption.
http://www.endeavors.com

The giFT Project
A modular daemon capable of abstracting the communication between the end user and specific file-sharing protocols. Features a homegrown p2p network, OpenFT.
http://gift.sourceforge.net/

Drumbeat
File-sharing program for the Mac featuring multiple servers and unlimited results.
http://drumbeat.info

WWW File Share
File sharing system with a browser-based client allowing sharing amongst closed networks of friends.
http://www.wfshome.com/

My Web Server
Free personal peer-to-peer web, file and application server that allows you to message, save your favorites-bookmarks, file upload, and save HTML pages in your shared directory.
http://www.mywebserver.org/us/

Myster
Open source utility for Mac, Windows and GNU/Linux platforms featuring a realtime, self-organizing and self-optimizing network. Its goal is to be distributed like Gnutella but far more scalable.
http://www.mysternetworks.com/

Iwannadownload.com
Run your own P2P program and this software to compare file names and sizes for their pre-qualified list of files. Increases your chances of getting a good file.
http://www.iwannadownload.com

MegaBrowser.com
Free peer-to-peer program that turns your PC into a web and ftp host so you can host your own sites and trade files. Built on IE plus has tabs, fetch, personalities, and search.
http://www.megabrowser.com/

Vladd44.com
BitTorrent and WinMX help site.
http://www.vladd44.com/

Gnomoradio
Music sharing, playback, and recommendation program for Creative Commons licensed songs. Gnomoradio is free, open source software for Linux/UNIX systems.
http://gnomoradio.org

Mute File Sharing
Multiplatform peer-to-peer file sharing network designed to maintain users' anonymity. Mute is free, open source software for multiple operating systems.
http://mute-net.sourceforge.net

WASTE
Software and protocol enabling secure distributed communication and file sharing for small trusted groups of users.
http://waste.sourceforge.net

Piolet
Music file sharing application supporting text and voice chat, multi-source MP3 and ogg downloads, and a built-in media player.
http://www.piolet.com

Acquisition
Shareware peer-to-peer file sharing program for OS X which connects to Gnutella and BitTorrent networks. Features list, support forum. Mac OS 10.2 or higher.
http://www.acquisitionx.com/

Soulseek
Free file sharing application. News, forums, FAQ and tutorials.
http://www.slsknet.org/

KCeasy
Open source Windows client built using giFT. Connects to the Gnutella, Ares and OpenFT networks. Site includes download links, FAQ and a forum.
http://www.kceasy.com/

The Poisoned Project
A free, open source file sharing application for Mac OS X that is able to connect to the Gnutella, FastTrack and OpenFT networks.
http://www.gottsilla.net/

GNUnet
Free (GPL) peer-to-peer framework of the GNU project with a focus on anonymous file-sharing. Works under Linux, BSD, OS X and Windows.
http://gnunet.org/

Filetopia
File sharing tool with public key encryption, instant messages, chat, free e-mail, message boards and file collection organizer.
http://host.filetopia.com/ft/index.htm

OpenP2P.com
O'Reilly Network's source for Peer-to-Peer (P2P) developer news and information. Topics include Napster, File-Sharing, Collaboration, Freenet, Gnutella, and P2P applications. Provides essential peer-to-peer articles and resources.
http://www.openp2p.com

Furthur Network
Network for sharing legally traded live music in MP3 and SHN formats.
http://www.furthurnet.org/

MLDonkey
Open source, multi-platform, multi-protocol client. Includes support for eDonkey2000, Overnet, BitTorrent, Gnutella and Fasttrack, and is written in Objective Caml.
http://mldonkey.sourceforge.net/

Shareaza
Open source multi-network P2P client for Windows. It is able to download a given file from the BitTorrent, Gnutella, Gnutella 2 and eDonkey networks simultaneously.
http://shareaza.sourceforge.net/

QP2M
Open source peer 2 mail application for Windows and GNU/Linux that lets users share, store and manage their files via e-mail accounts.
http://qp2m.sourceforge.net/

Omemo
Open source social storage platform in which users share anonymously files on a part of their hard disks. Includes a forum and a wiki.
http://www.omemo.com/

Phoenix Labs
Presents PeerGuardian, an open source IP blocker for Windows and Mac OS X that integrates support for multiple lists, list editing and automatic updates to protect users' privacy on P2P. Includes a wiki, a link to their IRC channel and a FAQ section.
http://phoenixlabs.org/

Ares Galaxy
Open source program for Windows which has its own network derived from Gnutella and which is also able to handle BitTorrent and Shoutcast.
http://aresgalaxy.sourceforge.net/

Shareaza Security Centre
Offers the X-Ray Security Filter designed to reduce spam and fake files; also hosts user guides on Shareaza and magnet links as well as a firewall checker.
http://www.shareazasecurity.be/

Zultrax
A peer-to-peer file sharing client running on both the Gnutella network and its own encrypted network.
http://www.zultrax.com/p2p/

PeerCast P2P Broadcasting
Open source, cross-platform software to listen to radio and watch video on the Internet. It uses P2P technology to let anyone become a broadcaster.
http://www.peercast.org/

Shareaza Plus
Derived from Shareaza, it has a redesigned network core developed in an attempt to provide better stability. Also aims to speed up file searches and downloads and has additional features for advanced users.
http://shareazaplus.sourceforge.net/

MXPie.info
Provides information, tutorials and several patches to make WinMX work since Frontcode Technologies abandoned its development. Also includes a support forum.
http://www.mxpie.info/

Winny in English
Provides a copy of the Winny P2P client translated in English. Also features screenshots, user guides and a link to the source code.
http://www.geocities.com/winnyenglish/