And not all GNU is Linux! Beyond the world famous GNU Hurd, there's also Debian GNU/kFreeBSD, and Nexenta (GNU/Illumos, which is the OpenSolaris kernel).
I think the most esoteric of them, though, is GNU Darwin (GNU/XNU). Darwin is the open source parts of OS X, including its kernel, XNU. There used to be an OpenDarwin project to try to turn Darwin into an actual independent operating system, but they failed, and were superseded by PureDarwin, which took a harder line against anything OS X getting into the system. GNU Darwin took it one step further and removed just about all of Darwin (except XNU) and replaced it with GNU instead.
This is my one gripe with Debian's installer. I don't mind it setting defaults like 27G for / and 10G or whatever for /tmp. But I don't like that you can't stop it from allocating the entire volume. If it left a few hundred GB unallocated, then it would be trivial to expand whichever one you realize you need to expand later on.
As it is, if you want to give more room to one partition or another later on, you have to shrink /home first. If /home is ext4, that's inconvenient. If it's XFS, though, it's a nightmare.