Nice start, Klaatu! I'll make sure to point 
junior sysadmins to this series!

So was the third option, which isn't really around anymore, Solaris? ^^
Because the OpenSolaris fork illumos is in fact, 6 years after Bryan Cantrill's "Fork Yeah! The Rise and Development of illumos" USENIX talk[0], still around. It's the base for distributions like Joyent's SmartOS and the database appliance Delphix ;)
And upstream for OpenZFS, too!

[0]: https://youtu.be/-zRN7XLCRhc