Not super obscure, but not many talk about it. Q4OS, I love it, a perfect windows replacement down to even imitating the old style windows installer. Plus it’s Debian based so it has a lot of support. I plan on moving my grandparents to it when windows 10 gets fully discontinued as their current rig doesn’t support 11
Longene Linux. Linux-based operating system kernel intended to be binary compatible with application software and device drivers made for Microsoft Windows and Linux.
Kiss linux. Gobolinux. They are both alien, but interesting, each one in its own way.
postmarketOS. Way too underrated.
Meego, a combination of Intel’s Moblin and Nokia’s Maemo. It only ever shipped on one device, the Nokia N9.