for people who want to try this with real hardware I would recommend the 3com 3c503 as the best choice of 16-bit ISA bus interface card. Or a real NE2000. There were some weird NE2000 clones back in the day that were not so great.
Other notable cards for older machines include the NE1000 (8 bit), NE2000, Intel 8/16, Western Digital or SMC 8000 series. Many PCI cards work well; just look for a packet driver. For those of you without real slots the Xircom PE3-10BT device is great, but they are getting more expensive in the wild.
SLIP and PPP work. PLIP works too, but I have not tested it myself.
And there are even packet drivers that allow for Token Ring and Arcnet to be used; they emulate Ethernet.
I also have a real NE1000 that I use in a Zenith Z-161 luggable, an XT class 8-bit isa machine. This is the machine I mostly use mTCP on.
https://github.com/Manawyrm/ISA8019
Seems like the common consensus is $10 scrapyard NIC plus Wi-Fi bridge. TBH, I was always surprised that the consumer Wi-Fi bridge was never a popular thing. You'd think it would sell more easily to customers, because most PCs have had Ethernet on board since like 2000, and even adding a USB dongle means having to bring new drivers in.
Now going full off tangent-- what happened to old wireless client hardware? If you go into any thrift shop, you're going to see a bunch of old 802.11g or n routers, but you usually don't see the adapters. I could see internal ones being scrapped with the PCs they were in, but I'd expect people who bought a new-spec router and matching adapter would replace them together.
generally it was built into laptops for 95% of the clients... Your typical Dell business laptop from the year 2000 came with a minipci slot and a 2.4 GHz antenna cable, populating the slot with an 802.11b card was an option.
or something like the original apple airport wireless AP and the wifi 802.11b built into macbooks from the era.
or in an even earlier era you would find like PCMCIA/PC Card type 2 or type 3 interfaces with an 802.11b radio and antenna in them to stick out the side of your laptop.
I actually have an 802.11b PCMCIA card sitting around. I bought it in 2003 because my university was rolling out a wireless network, accessible in about 1/6 of its surface area, and I was rocking a used Pentium II Thinkpad. Getting Slackware to handle 802.11 in those days was an amusing thing.
https://www.tindie.com/products/theoldnet/rs232-serial-wifi-...
There’s also pimodem http://podsix.org/articles/pimodem/