Regarding A Plague Tale, I used to work at Asobo Studio on the Engine/Tools team. That was during the Toy Story 3 / Disney Pixar Heroes period. The in-house engine is called Zouna and is very good. However, the piece of software that was the most interesting to me is their in house level editor called PAWAP (can't remember what the acronym meant) . It's a 20+ years old C++ codebase dating back to Kalisto (where most of the founders of Asobo used to work), of course modernised over time. I changed code that was written before C++98 was standardised! The Engine team is amazing there and it shows in the games.