https://medium.com/@donhopkins/the-shape-of-psiber-space-oct...
Was the idea with the direct stack manipulation dragging you describe to provide visual analogues to PostScript commands like roll/pop/etc?
It was very dangerous since you were editing the live data structures of the window system! The most complicated program I used it to debug was itself.
It was integrated with NeWS's multithreaded debugger, so when some process hit a bug or a breakpoint, you could "enter" the process and see what was on its stack, peek and poke at the objects, rearrange the stack and edit the objects, then send it on its way.
Since PostScript is homoiconic like Lisp, code and objects are made of arrays and dictionaries, which you could visually browse, edit, and execute. Very much inspired by Smalltalk, but with a twist of Lisp and FORTH!