Windows
Though I use Linux quite a lot, Windows is the most common user-facing operating system around. I have been using Windows since Windows 3.1, which is what my school used. Since then, I have used Windows 95, 98, ME, 2000, XP, 7, Vista, 8/8.1, 10, and 11.
For the server-side of Windows environments, my home lab is currently running Windows Server 2019, which is primarily used to learn about Active Directory. I have also used Windows Server 2003 and 2008. While my Windows Server installation does not currently handle DNS, it has been used as a DNS server in the past.
I also have Windows 11 Pro, which I have used to experiment with the Hyper-V virtualization software from Microsoft. It is only available in the Pro versions and above of Windows. It runs most of my experimental virtual machines that are only needed to test things, which normally get deleted immediately after the test.