The Dell Optiplex came with a Windows 10 Pro license. After using macOS as my main operating system for >7 years, coming back to Windows was really an astonishing experience -- especially, Microsoft Account integration is way smarter than an iCloud account, the latter of which basically requires you to log in to each app (FaceTime, App Store, Messages, etc.) separately. However, I had to say goodbye to Windows again in favor of a *nix distribution. Yes, I had tested out Linux Subsystem -- it's just not THAT well integrated.