DoubleDOS is a simple and easy to use multitasking tool for DOS. It
can preemptively run up to two DOS programs at a time. Its main
advantage is that it requires very little RAM overhead compared to
other multitasking or task switching environments. Because DOS
programs can and usually do bypass OS calls, many programs must be
"patched" in order to work.
things at once, then this would have been a good choice. Reportedly,
the first version may have worked with DOS 1.x.