There is something interesting (if you can say "interesting" to the idea of writing, say, an e-mail client in PostScript):
I remember some fuss being made about this in the early days of OS X, about "looking glass" (the gui system) using display postscript. Anybody know anything about that? If it's still a part of OS X or if it fell by the way side?
When Steve Jobs left Apple and started NeXT, he pitched Adobe on the idea of using PS as the display system for his new workstation computers. The result was Display PostScript, or DPS. DPS added basic functionality to improve performance by changing many string lookups into 32 bit integers, adding support for direct output with every command, and adding functions to allow the GUI to inspect the diagram. Additionally, a set of "bindings" was provided to allow PS code to be called directly from the C programming language. NeXT used these bindings in their NeXTStep system to provide an object oriented graphics system. Although DPS was written in conjunction with NeXT, Adobe sold it commercially and it was a common feature of most Unix workstations in the 1990s.
https://en.wikipedia.org/wiki/PostScript#History