It is the common root of RT11, CP/M and PC-DOS / MS-DOS, but also one of the only system that allows to run batch and time sharing tasks at the same time. IBM couldn't do that, if you needed time sharing, you had the 360/67 but then you couldn't run batches.
Fun fact, Microsoft originally used a KA-10 running TOPS-10 and cross assemblers for software development. The PDP-10 was also a cornerstone of developing NCP/IP, TCP/IP, and early AI.
It's fairly hard nowadays to find 36 bits machines still running, as the 8 bits byte has taken over the world. I think XKL uses an FPGA-based PDP-10 running TOPS-20 on its TOAD2 router, but that's about all I'm aware of.