Well, it supports all of Common Lisp incl. the whole numeric tower, Condition System and CLOS. If you know Common Lisp, it's all there. That means it's compatib

Well, it supports all of Common Lisp incl. the whole numeric tower, Condition System and CLOS. If you know Common Lisp, it's all there. That means it's compatible with much of the Lisp literature and thus automatically has a well-written specification for its core language. It provides an interpreter and a compiler. One can use it with GNU Emacs / SLIME. ABCL has also more the feel of what one would expect from Lisp, like an interpreter integrated with a compiler, useful backtraces, Lisp-like error messages and a Break-Loop REPL using the condition system. The compiler is written in Lisp. Thus it provides some more of debugging experience 'we' all love. It has much less users, less Java specific stuff, etc. It's also a bit slower than the typical native compiled Common Lisp.