The World of Peer-to-Peer (P2P)/Networks and Protocols
P2P Networks and Protocols 
This chapter will try to provide an overview of what is Peer-to-Peer, it's historical evolution, technologies and uses.
P2P and the Internet: A "bit" of History 
P2P is not a new technology, P2P is almost as old as the Internet it started with the email and the next generation were called "metacomputing" or classed as "middleware". The concept of it took the Internet by storm only because of a general decentralization of the P2P protocols, that not only gave power to the simple user but also made possible savings on information distribution resources, a very different approach from the old centralization concept.
This can be a problem for security or control of that shared information, or in other words a "democratization" of the information (the well known use of P2P for downloading copies of MP3s, programs, and even movies from file sharing networks), and due to it's decentralizing nature the traffic patterns, are hard to predict, so, providing infrastructures to support it is a major problem most ISPs are now aware.
P2P has also been heralded as the solution to index the deep Web since most implantations of P2P technologies are based and oriented to wired networks running TCP/IP. Some are even being transfered to wireless uses (sensors, phones and robotic applications), you probably have already heard of some military implementation of intelligent mines or robotic insect hordes.
Ultimately what made P2P popular was that it created a leveled play field, due to the easy access to computers and networking infrastructures we have today in most parts of the world. We are free to easily become producers, replacing the old centralized models where most of the population remained as consumers dependent on a single entity (monopoly, brand, visibility) for the distribution or creation of services or digital goods. This shift will undoubtedly reduce the costs of production and distribution in general as the price of services and products that can be digital transfered, the cost is now also becoming evident the quality will also be downgraded until a new system for classification emerges, this can be seen today in relation to the written media after the Internet impact.
FIDO net 
Electronic mail (often abbreviated as e-mail or email), started as a centralized service for creating, transmitting, or storing primarily text-based human communications with digital communications systems with the first standardization efforts resulting in the adoption of the Simple Mail Transfer Protocol (SMTP), first published as Internet Standard 10 (RFC 821) in 1982.
Modern e-mail systems are based on a store-and-forward model in which e-mail computer server systems, accept, forward, or store messages on behalf of users, who only connect to the e-mail infrastructure with their personal computer or other network-enabled device for the duration of message transmission or retrieval to or from their designated server.
Originally, e-mail consisted only of text messages composed in the ASCII character set, today, virtually any media format can be sent today, including attachments of audio and video clips.
Peer to Mail ( http://www.peer2mail.com/ ) is a FreeWare application for Windows that lets you store and share files on any web-mail account, you can use Web-mail providers such as Gmail (Google Mail), Walla!, Yahoo and others, it will split the shared files into segments that will be compressed and encrypted and then sends the file segments one by one to an account you have administration access. To Download the files the process is reversed.
The ecryptation was broken in Peer2Mail v1.4 (prior versions are also affected) - Peer2Mail Encrypt PassDumper Exploit.
Usenet is the original peer to peer file-sharing application. It was originally developed to make use of UUCP (Unix to Unix Copy) to synchronize two computers' message queues. Usenet stores each article in an individual file and each newsgroup in its own directory. Synchronizing two peers is as simple as synchronizing selected directories in two disparate filesystems.
Usenet was created with the assumption that everyone would receive, store and forward the same news. This assumption greatly simplified development to the point where a peer was able to connect to any other peer in order to get news. The fragmentation of Usenet into myriad newsgroups allowed it to scale while preserving its basic architecture. 'Every node stores all news' became 'every node stores all news in newsgroups it subscribes to'.
Of all other peer-to-peer protocols, Usenet is closest to Freenet since all nodes are absolutely equal and global maps of the network are not kept by any subset of nodes. Unlike Freenet, which works by recursive pulling of a requested object along a linear chain of peers, Usenet works by recursive pushing of all news to their immediate neighbors into a tree.
The File Transfer Protocol (FTP), can be seen as a primordial P2P protocol. Even if it depends on a client/server structure the limitation is only on the type of application (client/server) one run since the roles are flexible.
File eXchange Protocol (FXP) 
Zero configuration networking 
Zero configuration networking (zeroconf), is a set of techniques that automatically creates a usable Internet Protocol (IP) network P2P fashion, without manual operator intervention or special configuration servers.
Bonjour, formerly Rendezvous. A service discovery protocol by Apple Inc.'s. Bonjour locates in a P2P fashion, devices such as printers, as well as other computers and the services that those devices offer on a local network using multicast to maintain a Domain Name System record. The software is built into Apple's Mac OS X operating system from version 10.2 onward, and can be installed onto computers using Microsoft Windows operating systems. Bonjour also supports components that included other software, such as iTunes.
Bonjour for Windows ( http://support.apple.com/downloads/Bonjour_for_Windows )
Bonjour for Windows includes a plugin to discover advertised HTTP servers using Internet Explorer. If you have Bonjour devices on your local network with embedded HTTP (Web) servers, they will appear in the list.