Most operating systems have a common base including Unix, although it may have been around the longest. DOS was based on QDOS (Quick & Dirty Operating System) which used the UNIX syntax bur reversed the / too \.. C/PM also drew a lot from UNIX and was essentially a single user implementation, followed by M/PM as a multi user version.
The only unique operating systems that come to mind are UCSD/P system, FLEX and Turtle, all of which had similar tape/disk access commands to UNIX.
My personal favorite was ROM BASIC on the Sinclair (ZX80/81) that allowed you to embed HEX code in strings, and thus have total control of the hardware.
Alas we are in a field that moves so fast that we need to forget history in order to keep up and in the process we forget that mainframe and mini computers proceeded our own field.
Cheers
Chris