All powered by the Linux kernel, the very meaning of monoculture.
Also it isn't as if BSD, FreeRTOS, Aix, INTEGRITY, SmartOS, Illumos, QNX,... don't exist.
> Aix
This is more a limitation on the architecture - virtually nobody has power arch hanging around to play on.
I mean, AIX essentially _does_ not exist unless you happen to work in an enterprise or are in a similar environment that has it. It's not something to easily get your hands on – esp. not "as a kid".
But it’s not a monoculture because they’re wildly different applications of the technology.
It’s also not a culture at all because it’s a kernel.