The OrangeMicro cards, which are the best IMHO, did have a rather clever hack where every so often the Mac would sniff a frame from the PC card and update a window. Hardly realtime, but enough if you had a task you wanted to keep an eye on in the background. They also included a Windows app that did the same thing to the Mac.

I picked up a Reply DOS card the other day, the direct descendant of the original Apple DOS cards. Haven't tried it out yet, especially since the 7300 I use for this kind of hardware work is sort of wedded to my OrangePC 620 now (heat sink and all -- those K6-IIIs can sure get hot).