GNU/kFreeBSD
Hurd
IRIX


OpenBSD LiveCD:
http://g.paderni.free.fr/olivebsd/
(I don't know if it's still alive..)

Eh? I don't get it. 6th grade? What's that, 10 years old? It would take a super genius to develop calculus independently at that age. Hardly comparable to writing an alternative implementation of an existing OS kernel with a completely documented API.

I would of been 11 years old. I didn't develop it nor try to. I only came up with the idea of it.

You probably took that too literly

If Linux was never invented we would probably all be running on Hurd. Probably not really usable now but in this alternative universe the Linux developers would probably have gone with Hurd and developed for that instead, since afaik it was the only opensource kernel around at the time (I believe that BSD wasn't in the same form it is now? Although i'm a little rusty on my BSD history). It was the only GPL kernel on note anyway.

If Linux was to magically disappear tomorrow, it would be a tough choice between FreeBSD and Solaris. Really depends on how well Solaris supports my hardware (I ordered a free livedvd from http://get.opensolaris.org/ so ill find out soon), I know FreeBSD probably has better x86 hardware support. Also would depend on how well Solaris is GPLed. Sun might hold onto some core components etc... I would be interested to see how Desktop Solaris preforms against desktop FreeBSD and Desktop Linux.

GNU probably.
If it wasn't for the Linux kernel, I think the GNU team would have kept developing their kernel, if I understand that right.