There is also Illumos/OpenIndiana/OmniOS, basically continuations of OpenSolaris. I have used OpenIndiana for many years and it's been dead reliable and stable.

There is also Illumos/OpenIndiana/OmniOS, basically continuations of OpenSolaris. I have used OpenIndiana for many years and it's been dead reliable and stable. There's quite a few "quality of life" differences like boot environments (boot into a pre upgraded OS state, even years old), built in SMB server with NFS v4 style ACLs, dtrace, built in snapshot scheduling and management, and Napp-It is an available web UI for management a la FreeNAS/TrueNAS. It has a few differences, service management is quite different from other things, but overall very underrated as an OS I think.