Windows 3.0 was the first of the really popular versions of Microsoft's Graphical User Interfaces (GUI).  Its last version is 3.12.  Even though you could open multiple windows, it was still a single tasking system.  Also, it ran as an application itself under DOS and therefore, doesn't really qualify as an Operating System.

Windows 3.1x allowed the user to open multiple windows for different applications however, once another window was opened the application in the previous window would pause until it became the current window.   Therefore,

Microsoft has stopped providing any further updates to Windows 3.12.

A few years ago, Internet Service Providers (ISP) were supplying custom software that enabled users to access the internet, however, most ISPs that I've talked to today are no longer support the Windows 3.1x versions.

Anyone still running the Windows 3.1x systems should really consider upgrading.