Reading this thread, I just remembered that I used to have an old IBM PC Jr that ran DOS (years earlier), a great machine hardware-wise (though it was not a marketing success, I've read). And some time back I had written this post about it:
Lissajous hippo, retrocomputing and the IBM PC Jr.:
https://jugad2.blogspot.in/2012/09/lissajous-hippo.html
While looking up info about the PC Jr. for that post, I came across Mike Brutman's PC Jr. page (mentioned in my blog post):
He was an IBM employee for a long time and so had access to good info about the PC Jr. - both hardware and software, and his page above is one he maintains about that machine - a sort of retrocomputing site about the Jr.
We then talked some on email, and he told me he had built a TCP stack for DOS and was running it on his Jr. That page is here:
http://www.brutman.com/mTCP/mTCP.html
He says others are also using mTCP, for fun, work and even business.
Here's an excerpt from his overview section about mTCP:
[1]:
[ mTCP should run on all variants of DOS including IBM PC-DOS, Microsoft MS-DOS, DR-DOS and FreeDOS. All of these applications will run well on the oldest, slowest PC that you can find - I routinely use them on an IBM PCjr made in 1983 because nothing beats the fun of putting a 30+ year old computer on the Internet.
People are using mTCP for goofing off and for real work. If you have a DOS machine that needs to send data across the network mTCP can help you get that done. Besides its utility to vintage computers I have heard of people using it to transfer lab data from dedicated industrial PCs, allowing backups to be run on old machines, and sending sales reports from the branch offices of a retail store to a central server.
Don't have a vintage computer laying around? No problem! mTCP applications will run in a variety of virtual and emulated environments. It has been tested with DOSBox, SwsVpkt, VirtualBox and VMWare. See the documentation for the details. ]