I like to study the screenshots of Interlisp applications in research papers to learn how the GUIs were put together, what APIs and tools they used, and how to code something similar.
The screenshots of the user interface of an expert system shell in this paper are especially clean and legible, which is unfortunately not often the case for old papers.
https://bitsavers.org/pdf/stanford/Stanford_CS_TR_Collection_2025-12-12/PDF/1985/CS-TR-85-1068.pdf