Depends entirely on what kind of hacking you want to do. If you want to pull out parts that are portable Common Lisp and use those, you're free to do so. If you

Depends entirely on what kind of hacking you want to do. If you want to pull out parts that are portable Common Lisp and use those, you're free to do so. If you want to hack the code so the whole thing compiles on SBCL, you're free to do that too. Similar situation to free-software apps whose developer targets OSX: no legal barrier to using the code on Linux, but may take some work.