Tribblix is an operating system distribution derived from OpenSolaris, OpenIndiana, and illumos, with a retro style and modern components. The base kernel and commands are from illumos, with a few components currently repackaged from OpenIndiana (mostly X11, some other oddments); pretty much everything else has been rebuilt from scratch.
SunOS was my first commercial UNIX, and part of the reason I love using FreeBSD now is owing to its tooling and design that have been influenced from the Solaris world. I have yet to use Tribblix in production anywhere, but I keep it around in a VM for tinkering. It’s excellent.
Thanks to Michael Dexter for recommending it at AsiaBSDCon 2018 :).