In addition to the compiler and runtime system for ANSI Common Lisp, it provides an interactive environment including a debugger, a statistical profiler, a code coverage tool, and many other extensions.

[1] The name "Steel Bank Common Lisp" is a reference to Carnegie Mellon University Common Lisp from which SBCL forked: Andrew Carnegie made his fortune in the steel industry and Andrew Mellon was a successful banker.

[2][3] The main point of divergence at the time was a clean bootstrapping procedure: CMUCL requires an already compiled executable binary of itself to compile the CMUCL source code, whereas SBCL supported bootstrapping from theoretically any ANSI-compliant Common Lisp implementation.

[2] The original rationale for the fork was to continue the initial work done by Newman without destabilizing CMUCL which was at the time already a mature and much-used implementation.

Since then SBCL has attracted several developers, been ported to multiple hardware architectures and operating systems,[4] and undergone many changes and enhancements: while it has dropped support for several CMUCL extensions that it considers beyond the scope of the project (such as the Motif interface) it has also developed many new ones, including native threading and Unicode support.