For fun and for knowledge, what else?

because 3 operating systems apple-linux-windows isn't enough! Just like the 3 web browsers webkit-mozilla-chromium isn't enough. Remove the derivatives, and there aren't really that many different freshly updated and fully functional desktop / phone operating systems available, but it's good to see some. Thank you https://www.redox-os.org/

https://serenityos.org/

https://www.openbsd.org/

https://wiki.osdev.org/Projects

Let's also add https://genode.org/ to the list :)

Don't forget about GNU Hurd. ;)

minix3

Well, sometimes people make OSes for commercial use, educational use, etc.

Yep, all those too :D

Because UNIX and its derivatives do suck. (huge TCB, drivers in the kernel, global namespaces, ambient security)

Therefore, it is sensible that other approaches are being considered.

> Because UNIX and its derivatives do suck. (huge TCB, drivers in the kernel, global namespaces, ambient security)

This is a unix-like, and none of those are inherit to unix/derivatives; there are small unixen, there are microkernel unixen, containers are popular, and whatever security model you want, someone has hacked it onto an existing unix-family OS.

> Because UNIX and its derivatives do suck. (huge TCB, drivers in the kernel, global namespaces, ambient security)

GNU Hurd on drivers, you can use the ones from GNU/Linux I think. On global namespaces, I'd say Plan9/9front it's Unix 2.0.

That is a good question

Why not?