Ranked in these QuestionsQuestion Ranking
Pro Fast native code compiler
SBCL (and CMUCL)'s compiler, Python, produces optimized native code.
Pro Free Open Source Software
Parts of SBCL are licensed under a BSD-Style license. The rest are in the public domain.
Pro Actively maintained
Bug-fixes, performance improvements, refinements. New ports.
Pro Type inference and type checking
Incorrect type declarations are treated as errors. SBCL can deduce types quite well.