There were many available in that timescale. QNX DR Concurrent CPM which became Concurrent DOS DR FlexOS PC-MOS I seem to recall seeing a few others advertise

There were many available in that timescale. QNX DR Concurrent CPM which became Concurrent DOS DR FlexOS PC-MOS I seem to recall seeing a few others advertised in magazines at the time. As to DESQview, it had DESQview/X as an addition. As to unique bits, what OS/2 had was memory protection, but then so did QNX and FlexOS, I'm not sure about PC-MOS.