It was called the "AT Gizmo". The original design would only plug into a few other systems beyond the IBM AT. A newer design would fit about 80% of the 286 machines on the market at the time. It was mainly designed for PC-MOS's predecessor, Multilink, although it would work with PC-MOS, sometimes.

Yes. It did. Lotus 2.01 was one of our primary compatibility test programs. Word Perfect 4.2 was another one we tested a lot.

I worked in tech support Software Link and maintained the BBS way back then. At one point I had a backup of the forums but I probably tossed it out with my 3.5" floppy collection years ago. I guess I should have kept it around. Supporting PC/MOS was a nightmare. Fielding calls all day from angry users and vendors was very stressful and frustrating. 30 years later, I still hate answering the phone.

At a company I used to work for we found that EBay was a great place to buy old equipment we required for our outdated, but still needed, systems (mostly to connect to scales and such). You do need to use a lot of caution when buying there since the quality of the equipment and the quality of the sellers vary a lot. There are also some sellers who have separate online stores where they feature a wider variety of items in order to avoid fees. You may also find someone who sells online also has a physical store location in your area. Visiting a tech graveyard store is a fun way to blow an afternoon. I do agree though with what AmiMoJo said, virtual machines and cost/benefit analysis is going to be better in the long run than trying to keep that IBM AT running.