I don't know what your threshold for "cool" is, but an example of something that's straightforward in Lisp is if you want to generate a hierarchy of class declarations from a schema, so the classes have certain instance variables and methods defined in some regular way; for instance, you might want to auto-generate a method for each class that returns a collection of the values of certain of its instance variables. In most any language other than Lisp, you'd have to define your own schema syntax and write a parser for it and a generator that outputs the declarations in the target language. In a nutshell, it would probably be painful enough that you wouldn't bother; you'd just type in all the boilerplate manually. In Lisp, not only is writing such a schema translator relatively straightforward, but you get incremental recompilation for free.