• CP-V (Control Program fiVe---Xerox Sigma 6/7/9, etc.)
• DOS (Windows 3.x is an environment/application).
• Windows 95.
• Windows NT
• OS/2 (and OS/2 Warp).
• Unix (and it's variants).
• Linux at Andrews.
• Solaris 2.5. on UltraSparc, Pentium Pro, PowerPC by Sun.
• Check this for security info.
• Macs have an operating system, but why would I care?