[that_jojo]

VMS feels like DOS if DOS were actually secretly UNIX

Also, don't forget about OS/8 for the PDP-8 series. Very DOS-y, and released by DEC all the way back in '71.

[icedchai]

VMS feels like DOS if that DOS was from another dimension. About the only thing they have in common is "DIR" and ".EXE" extensions.

[WorldMaker]

Which is also why it's so fascinating Windows NT sort of merged both parallel dimensions with its influences directly from both DOS and VMS.