I have used a DR-DOS 7 that was set up with a nice task switcher, between terminate-and-stay-resident programs ( not true concurrent processing ).

This setup started WP5.1, a spread sheet -- I think Lotus123, and a graphics editing program. I think it switches using cntrl and the F keys, similar in feel to how a linux machine switches consoles.

I think at the time this was set up, only DR-DOS could do the task switching. I don't know if that is still true.