Never used that one. Makes sense though since NT grew out of research on OS/2 v3. The Posix subsystem[0] didn't work so well the times I tried working with it. The OS/2 subsystem didn't matter so much as Windows NT popularity outgrew that of OS/2 pretty quickly.
If they open sourced the POSIX subsystem, it might have had a chance to keep growing.
https://second.wiki/wiki/2-subsystem