system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are Windows, OS X, and Linux the main operating systems out there? Why are there no newer operating systems?
gpt
there are many others.   those 3 are the big consumer OS's.   there are many other backend industrial OS's that are still in use like VAX.

Linux is a branch of the *nix family of OS's.  Other members of the *nix family include the BSD branch, the Solaris branch, the AIX branch, among others.   There are many many published flavors of Linux in its branch,   Redhat, Gentoo,  Centos,  Ubuntu, etc.      Other branches have multiple members as well,  FreeBSD, OpenBSD, NetBSD, etc.   

It takes alot to make an OS.   you need not only the working core, but you need vendor support.    The Linux branch in its infancy had quite a problem with consumers because no vendors published hardware drivers for it, because there's not enough market share of consumers.  it's a catch 22.