[Duck]

Here is a list of well-known operating systems. A few might be missing.
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Windows:

• MS-DOS
• Windows 3.1
• Windows 95
• Windows 98
• Windows 2000
• Windows XP
• Windows Vista
• Windows 7
• Windows 8 / 8.1

Linux:

• Ubuntu
• Mint
• OpenSUSE
• Fedora
• Debian
• CentOS
• Gentoo
• Red Hat

Mac:

• OSX Leopard
• OSX Snow Leopard
• OSX Lion
• OSX Mountain Lion
• OSX Mavericks