Incidentally after years of resisting last time I updated my resume I removed every reference to UNIX and almost everything else non-Linux. I realize there are still jobs out there where it's a in-demand skillset but it just sounded dated, braggy, fabricated to mention my past experience with HP-UX, AIX, and Solaris in a world where it won't be relevant for 99% of the jobs I'm applying for. Also it's been so long since I worked with them I'm not even sure I can confidently claim them as legitimate skills anymore even if an employer felt they were valuable.
For every POSIX operating system that has been removed, ten have been added.
Both Haiku and OpenVMS would count. We could even throw in Windows.