Oh then it's interesting because I thought it required to use their IDE. With Emacs/Slime, is it as integrated as with sbcl for example?
No, you may still want to use the IDE to access functionality that is not available through slime. But you have the choice. According to the slime documentation: "Most features work uniformly across implementations, but some are prone to variation. These include the precision of placing compiler-note annotations, XREF support, and fancy debugger commands (like 'restart frame')."