Well, my beard is the right colour… But none.
I had an Acorn BBC B (running Acorn MOS), then an A3000, A5000, RiscPC (all with RISC OS), then I switched to Linux. I have occasionally used DOS and Windows at work, but never as my main home OS. (I write Linux software for work, but do use a windows laptop to connect to my Dev box)
It’s widely used in the EDA (chip design) industry. (Unfortunately)