Steel Bank Common Lisp is an open source Common Lisp implementation. It provides an integrated native compiler, interpreter, and debugger. SBCL is a fork off of the main branch of CMUCL. SBCL is distinguished from CMUCL by a greater emphasis on maintainability. In particular, the SBCL system can be built directly from its source code, so that the output corresponds to the source code in a controlled, verifiable way, and arbitrary changes can be made to the system without causing bootstrapping problems. SBCL also places less emphasis than CMU CL does on new non-ANSI extensions, or on backward compatibility with old non-ANSI features. Support for native threading on GNU/Linux is available for the x86 and amd64 platforms using an NPTL enabled GLIBC. SBCL 0.8.17 and later support Unicode.