Clozure CL and SBCL are great. I use both. It's just that LispWorks comes with batteries included, has a cross-platform GUI toolkit, has a cross-platform GUI-b

Clozure CL and SBCL are great. I use both. It's just that LispWorks comes with batteries included, has a cross-platform GUI toolkit, has a cross-platform GUI-based IDE, has a great runtime, has more delivery options, makes great use of CLOS, has more tools included, ... There is a noticeable step up in features from the typical open source / free software implementations to something like Allegro CL or LispWorks. Since both a proprietary and relatively expensive, often they are not a choice. But the fact remains, that they offer more and better features. SBCL shines with some features of its compiler. The topic is discussed, because for some people it is difficult to understand why one pays thousands of dollars for development and/or runtime (see for example the Azul JVM which starts at $3500 per machine per year).