exit-hooks provides a portable way to automatically call some user-defined function when exiting Common Lisp (both quit from the REPL or a kill in a shell). Like atexit in C and Python or Java’s Runtime.addShutdownHook(). It currently supports SBCL, CCL, ECL, ABCL, Allegro CL, clisp and CMUCL. Before exit-hooks, there was no portable way of doing so and no staightforward way to use an exit hook on ABCL. It can be used for tasks like parmenantly save something when exiting Lisp.