|You don't need to use wired Ethernet or WiFi to connect your computers together. While those are usually the fastest and most reliable methods, there are alternatives.
USB Networking Cables
You can connect multiple computers via their USB ports. To do this, you need a special USB networking cable. This cable essentially acts as an Ethernet crossover cable. However, instead of using the networking port on your system, you would use USB ports on each system. It works well if you need to connect a laptop to a nearby desktop computer to sync up files.
There are three major drawbacks to this method. The first is the limited range. USB only offers reliable connections up to about 30 feet without a repeater to amplify the signal. Second, the system essentially connects computers into a chain so the units on each end have to communicate through those units in the middle. Finally, the special USB cables needed are quite espensive if you plan to use them to connect more than two computers together. If you have several systems to connect together, wired or WiFi Ethernet is a better way to go.
Phone Line Networking
This method uses your phone lines to connect computers together. Since most people have phone jacks in most rooms of their homes, it saves running network wiring to those locations.
As you woiuld expect, phone line networking is rather slow. In the end, physically moving items from computer to computer using a disk may be quicker.
Power Line Networking
Power line networking is another method of connecting computers that avoids having to run wiring. You plug your computer into a wall jack via a special adapter and your home's electrical lines become network wiring.
Like phone line networking, this method tends to be rather slow.
Serial or Parallel port connections
These are the absolute slowest form of connections. However, connecting through either port can allow even older computers to talk to each other. You'll need special cables in order to connect two systems together.