Don't know about any DOS game but Diablo 1 (a windows game) supported daisy-chained serial like this.

You can find some utilities to play Doom and other games (heretic, hexen) with 3 or 4 machines connected via null modem cables at https://www.doomworld.com/idgames/utils/serial/

lolo799 wrote on 2023-12-18, 22:37:

You can find some utilities to play Doom and other games (heretic, hexen) with 3 or 4 machines connected via null modem cables at https://www.doomworld.com/idgames/utils/serial/

I remember using JServe02 listed there to get 4-player Doom working in the mid-1990s. A friend and I each had 2 phone lines and 2 modems but it looks like it supports null-modem cables, too.

Some network software of the early 90s did indeed support chained serial connections.
I remember Kirschbaum Link and the more advanced version version, Kirschbaum Netz (based on Little Big LAN aka the $25 network or the $75 network).

Many thanks for all the answers. I finally did it and it was awesome. I recorded on my youtube channel:
First time with 3 x IBM retropcs: https://youtu.be/EcTvMwa6Mbs?feature=shared
Two Windows DirectDraw games, Diablo 1 and Starcarft 1, have built in 4 players direct cable connection multiplayer. I do own 4 x IBM retropcs, but I didnt had any more players. My other friends that are into retro were away in holiday, so I had to use my two brothers.
The second time I used 3 x 486 dx2 66mhz: https://youtu.be/eB7FK8w-L2E?feature=shared
This little ms-dos program called HX8 (made by Armin Rigo) is wonderfull: https://www.doomworld.com/idgames/utils/serial/hx8
It was specially done for Hexen 1.1 for up to 8 players chained with serial cables. But works for up to 4 players in Doom and Heretic. The program HX8 is affected by the over 200 mhz bug. So if you use a powerfull pc, you have to slow it down.
Again, it can be done with 4 players, but I didnt had any more players, because I recorded in the same day with the Windows games.
I am just an amateur passionate about retro, not a professional youtuber. So my apologies for the bad audio or the boring lenght of the videos.
I recorded in hope to inspire other people to grab some serial null-modem cables and play multiplayer games with their spouse, kids, brothers, friends etc.
There are soo many games, up to year 2000, that have 2 players serial direct cable connection multiplayer, it is soo simple, there are no drivers to install or setup, and those serial null-modem cables are still available cheap in online stores.

I once tried to play a 3-player game of Warcraft 2 using multi-link setup. I had two Windows 95 PCs connected to an Ethernet switch at my place and another one at another location. I have set up a dial-in IPX over PPP link one of my PCs and asked the remote location to dial me using their modem.

To my surprise it didn't work as I expected - the game was able to communicate either with another PC on my LAN, or with the remote PC over the modem (but never with both), and the behavior depended on whether I start the game before or after picking up the call originating from the remote modem. I wasn't very experienced in computer networking so I wasn't able to collect any troubleshooting information back then.

I remember doing it with Doom but not natively. Some utility was used to fake an ipx network over null modem cables.

b0by007 wrote on 2023-12-18, 20:55:

Did I read it on some false game advertising, or was that on some early revision, like youtuber Tech Tangets discovered about doom v 1.1 having multimonitor gameplay?

Yes I did a post and video on this back in 2018, Even has a link to a downgrade patch for other versions of doom back to 1.1
Vanilla / Dos Doom in 3 screen mode. I finally did it!

Not quite related to your question but Wackey Wheels only supports Serial if you want multiple computers, no IPX. Thats my excuse to have a null modem cable around even though all my computers are networked