DOS / OS
EN
Citrix Multiuser 1.0
This is Citrix Multiuser 1.0. It's based on Microsoft OS/2 1.21. It only supports serial terminals, but it is a multi user version of OS/2 for 386 and higher computers. This is very rare and hard to find, complete with documentation, disk images.
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OS/2 / OS
EN
Citrix Multiuser 2.0
This is Citrix Multiuser 2.0, based around OS/2 2.0. The big change is that this can run MS-DOS based applications, and includes DPMI support so, yes you can run DOOM! Additionally Windows 3.0 in standard mode is supported.
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Windows NT/2000 / OS
EN
WinFrame 1.8
Citrix WinFrame provided remote desktop and application tunneling on a customized Windows NT 3.51.
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