Windows 7
Windows 8.1
ChromeOS :D i dumpped windows back in 2012.
I'm currently using Windows 7 as I think it's one of the better ones but will soon be switching to Windows 10. I did some beta-testing on 10 and was really impressed. It has the speed of 8 and all the good features of 7 and XP and it's really easy to use. Microsoft finally has a real winner.
Windows 7
Why would an anonymous person need to know what operating system we are using? Without a reason for the question, I hesitate to articulate and answer... As I suspect nefarious reasons for this snooping!