SGI IRIS 2000
sgi iris 2500T
sgi iris 3130
https://en.wikipedia.org/wiki/Sun-1
https://en.wikipedia.org/wiki/Sun-2
https://en.wikipedia.org/wiki/Sun-3
https://en.wikipedia.org/wiki/HP_9000
https://en.wikipedia.org/wiki/HP_series_80
https://en.wikipedia.org/wiki/HP_9845C

note that some of these are 68000-based systems, and a few of those I want to look up for my own interests — especially since those would probably will just suffice with the GTK+ 3 port assuming a modern unix-like system can be run on them