Alt text:
Twitter post by Daniel Feldman (@d_feldman): Linux is the only major operating system to support diagonal mode (credit [Twitter] @xssfox). Image shows an untrawide monitor rotated about 45 degrees, with a horizontal IDE window taking up a bottom triangle. A web browser and settings menu above it are organized creating a window shape almost like a stepped pyramid.
Edit: alt text
I think "popular" is stretching it here, Debian GNU/kFreeBSD is dead now, and while Hurd is interesting, it has ways to go.
Alpine is actually popular, particularly as a lightweight host OS to run docker.
Honestly, I think the only interesting micro kernel right now is Redox OS.
I just imitated your tone with 'popular' didnt mean anything much.