Siemens is also very much in on this. Up to about the 90s most of these vendors were running stuff on proprietary software stacks running on proprietary hardware networked using proprietary networks and protocols (an example for a fully proprietary stack like this would be Teleperm). Then in the 90s everyone left their proprietary systems behind and moved to Windows NT. All of these applications are truly "Windows-native" in the sense that their architecture is directly built on all the Windows components. Pretty much impossible to port, I'd wager.