One of the easiest protocols to use.
In 1984, Apple released the Macintosh. On the back were two serial ports. You could connect printers, modems, or to one another, like Ethernet crossover. It was the first PC to have built-in networking support. At the time, 3Com was charging $1000 for PC Ethernet cards.
The protocol for Apple devices (PCs and Stylewriter/Laserwriter printers) was known as Appletalk. It was incredibly simple to use, and still is. You plug in one computer to the other, turn Appletalk and file-sharing on with the radio buttons and enter a password. There is no step 3!
In later versions of Mac OS, like after version 5, you would open the Chooser and select the computer/printer to connect to, as well as turn on and off Appletalk. Things like the Sharing Setup control panel let you turn on and off Program Linking and File Sharing. Later on MacTCP came out (Way before Windows or DOS got IP addressing), and you could configure an Internet connection.
The Serial cable protocol was called localtalk, and one could interface with plain phone wire as cable. Ethertalk was Appletalk with the Ethernet cable. You could also do Appletalk with Infrared(IR).
There is no need to enter in IP addresses, it's not TCP-based. You just plug your computer into the network and you're instantly available to the other computers. I believe it broadcasts its presence over the LAN to the others, and all the computers on the network respond to a ping, which is why you can see them all. In large networks there are Zones, like Subnets or workgroups in Network Neighborhood.
The great thing about it is that it has had no updates. The first 8MHz Mac from 1984 can work perfectly with a 2002 Dual 1 GHz G4 server. Microsoft has built support for Appletalk into its Windows NT software. Various software bundles like Dave let you connect to a Mac volume from a PC with Appletalk.
In 1999, Apple bought technology from Open Door Networks and created an Appletalk over TCP/IP option in Mac OS 9, enabling file sharing over the internet. In addition, you could remote script events over Appletalk, so that you could send files from one computer to another, then run an Applescript to make Photoshop batch process the folder and upload them to a web server, all done remotely.
Sharing a Mac with Appletalk is one of the safest things (provided you use a good password). First, the majority of users don't use it, as they don't have a Mac. Second, since it's not TCP/IP based by default, it doesn't go past the router or onto the internet. I managed to setup a file sharing system where three computers all shared files without a password, and are all completely safe from outside hackers.
Apple is downplaying the technology now, as they feel TCP/IP based file sharing is the future. It's still supported in Mac OS 9 and Mac OS X, but it's a legacy technology today. Many SysAdmins didn't like it becasue it was slower than the TCP, and sent lots of broadcast packets to one another announcing themselves.
Now for networking Apple is using AFP, Apple Filing Protocol. It doesn't Auto-discover other clients, but it works accross the internet.
Apple has realized that Appletalk's major strength (that users love) is it's ease of setup and Auto-discovery. At Apple's Developer conference 2002, WWDC, they announced that OS X will have a new software they call Rendezvous. Apple claims that you can plug any OS X enabled Mac into the network and it will be discovered by the other computers. Think of it as being just like Bluetooth, files will automatically transfer and music and videos will be broadcast. It's based on DirectConf and an Open Standard no less, so we might see it working with Windows XP.
Rendezvous, Apple’s proposed new industry standard for automatic discovery of computers, devices, and services on IP networks, promises to make heterogeneous networks as easy to use as AppleTalk networks. Also called ZeroConf, Rendezvous lets your hardware configure itself on networks using the Internet Protocol, tell other devices which services it offers and discover devices on the network, as well as their associated services. You can connect your devices together however you like — wirelessly over AirPort or Bluetooth and by physical connections such as FireWire or Ethernet. Of course Rendezvous works for printers and file sharing, but that’s hardly innovative. As a technology demo, at WWDC 2002, Apple showed the use of Rendezvous to make iTunes into a music jukebox for your whole house. You could keep all your music on the iMac in the den, and then listen to the iMac’s playlists using iTunes on your iBook connected to the living room stereo.