Microsoft Windows 3.0
Microsoft Windows 3.1
Microsoft Windows 3.11
Microsoft Windows 3.11up (Which is a update for 3.1)
Microsoft Windows WFWG (With extra network features)
There is little difference between Windows 3.1 and 3.11, an update is available. Windows for Workgroups 3.11 is only really of benefit if you are on a network.

The 3.11 upgrade is free and used to be available for download at the Microsoft Website. The file is called WW0981.EXE, and it contains updated versions of: krnl386.exe
user.exe
gdi.exe
shell.dll
commdlg.dll
vtda.386
pscript.drv

Overall, 3.11 is faster and more stable. It also has a print spooler for faster printing.

If you can't find it at M$, search in google for WW0981.EXE.

There are in fact Windows versions 3.1 and 3.11 as well as Windows for Workgroups versions 3.1 and 3.11 each is an update on the 3.1 versions. Windows for Workgroups is only really of use if you plan to network windows, but will run in standalone mode!

Windows 3.1 - the 'bread and butter' version (dated 03/10/92)
Windows 3.1 for Workgroups - dated 10/08/92
Windows 3.11 - a very rare update on 3.1 (12/31/93)
Windows 3.11 for Workgroups - the other common Windows version (11/01/93)
Windows 3.11 for Workgroups with TCP/IP stack - shipped with NT 3.51 server (05/26/95)

3.11 and 3.11 for Workgroups are completely different versions. 3.11 has *no* network capabilities.
3.1 for Workgroups and 3.11 for Workgroups are slightly different in memory management, 32bit access, and network installation/tools. In fact, 3.1 for Workgroups has got an internal version # "3.11 beta".