Back in... around 2000, I ported the Hercules mainframe emulator to AS/400.
Cue jaw-dropping and apoplexy in IBM, at the prospect of being able to run S/390 & z/Series software on AS/400 :-)
Oh and free trivia... Did you know the AS/400 was nearly called the System/40? Seeing as how it was a direct descendant of the System/38... but also had some compatibility with the System/3 / System/32 / System/34 / System/36 line...
And yes I have one of each, all pretty much up and running :D -