Windows Subsystem for Linux (WSL) which lets you basically run linux kernel along side the windows kernel which lets you do a lot of cool stuff like containers, linux apps, whole DEs, etc.
It was pretty cool for like 5 minutes until people realized that keeping windows around was kind of pointless and we should just be running pure linux lol.
It's still a good feature, but it just gives you a direct comparison of linux vs windows which tends to outshine windows.
That's mostly fluff though. Like you show, the core is either Linux or bsd and gnu, and then you have a handful of families.
That's not fragmentation, that's freedom.
And compatibility is a big factor too. Because of gnu and posix basically, almost anything that works on one distro will work on another.
Imagine if each distro was completely locked from anything on another one. That would be fragmentation, and we wouldn't be talking about it, because it would be shit.
You basically have BSD and Linux and in the Linux space {glibc/musl systemd/openrc/runit PKGBUILD,ebuild,deb,rpm} which seems like a lot but it’s the really niche stuff that’s fun to pull apart and play with.