You must be one of those people who think that there are three operating systems in the world, four if you count BeOs.
How many are there? I count at least in the hundreds, at least if advanced research projects are included.

My post was a bit flamebait, but OS pundits have run around for years claiming that "the next big thing in OS design is XXX", and been wrong nearly 100% of the time when their claims don't reflect computer science research.

UNIX is still a modern system because its design is not impeding new developments within it in any way. (At least that I have been made aware of.)