I still remember connecting two MS-DOS computers together with a parallel cable, that was the easiest way to do "large" file transfers there for a while (used a program called LapLink, iirc)...
Where Laplink isn't really a network, just a file transfer thing that requires Laplink to be running on both PCs, PLIP is a network driver that lets you do all the usual network things over the connection.
And since PCs can have up to 3 parallel ports before things start getting stupid, it's pretty straightforward to have a row of machines with PLIP links going both ways, bridging or routing the interfaces. Or, do PLIP-SLIP-PLIP-SLIP without adding any ports, and you could have a functional-but-brittle-and-slow network for pennies.
I was running that in the nineties. My main desktop, running Linux, and an ultra old, ultra crappy laptop running Linux too. They'd be connected using PLIP and the desktop, more powerful, was running its own X server but also applications for that were running on the laptop's X server.
So my brother and I could both be using Netscape to surf the net (we'd call it that back then) at the same time, over the 33.6 modem connection.
It was really easy to run PLIP and was saving me the trouble to try to get network card running under Linux on my desktop and most importantly saving me the trouble to try to get the PCMCIA crap to work on my laptop.
Fun times...
P.S: and, yup, back then laptops had a full parallel port!
Nope but I would loved that back in the days: we created a LAN between our house and the (attached) neighbors' house (so we could play Warcraft II against each other) but... We couldn't create a LAN with the neighbor across the street!
Once around 2005-ish, I scored an 802.11b client-bridge real cheap because .11g stuff had been out a while. Velcroed it to the lid of my Zenith Supersport, and made a ten-inch ethernet cable to connect it to the PE3. An unholy abomination allowed both units to tap power from the keyboard port; the less said about that, the better.
What felt like thirty hours of hair-pulling later, I had a 720k DOS boot disk with packet drivers and a telnet client, and I could MUD from my lap, wirelessly. Ahh, the sweet smell of useless success.
Then like an idiot, I sent all that stuff to the recycler around 2008.
Edit: Yes, I'm aware that box says RS-232, but with gender-changers, the dip-switches and some cable-bridges, you could abuse it for 'parallel'.
My favourite was bootstrapping using 'COPY /B COM1: C:LL3.EXE' to get the Laplink executable to the target machine over Serial, when you didn't have a spare floppy.