The question is too generalized. There are two kind of OS; Network OS and Desktop OS. DOS, Windows 9x/me, XP Home/Pro, Win2kProf and earlier version of Redhat and other Linux variants will fall on Desktop OS.

Novell, OS/2,WinNT4/2k/2k3, Solaris, Redhat AS, Linux Variants and SVR4 Unix falls on Network OS cause they run on purposes for Network users.

Windows 3.11/WFW never been an OS cause they run on top of DOS.