It’s hard to be categorical but for me: compilers, mathematical software, autonomous or long-running software, high-performance code, data structure-heavy code.

It’s hard to be categorical but for me: compilers, mathematical software, autonomous or long-running software, high-performance code, data structure-heavy code. Some of my former colleagues might try to convince you Lisp is a great choice as a backend language. I agree that it’s a great choice in isolation, but I don’t have tons of experience using other tech to build extensive APIs with tons of layers. A little more meta, but Lisp can be a great choice if a project can only afford a handful of developers. Lisp can give you the “bang for buck” in terms of code output/productivity and comprehensiveness of the solution to a problem.