Steel Bank Common Lisp is a development environment for Common Lisp, with excellent support for the ANSI standard: garbage collection, lexical closures, powerful macros, strong dynamic typing, incremental compilation, and the famous Common Lisp Object System (multimethods and all). It also includes many extensions, such as native threads, socket support, a statistical profiler, programmable streams, and more. These are all available through an integrated, interactive native compiler which feels like an interpreter. SBCL is unique in being a multiplatform native compiler which bootstraps itself completely from source, using a C compiler and any other ANSI Common Lisp implementation.
Common Lisp Quick Reference is a booklet with short descriptions of the thousand or so symbols defined in the ANSI standard. It comes with a comprehensive index. It is written in LaTeX and formatted for printing on both A4 and letter paper. After folding the sheets lengthwise, they can easily be turned into a handy booklet.
ACL2 is a mathematical logic, programming language, and mechanical theorem prover based on the applicative subset of Common Lisp. It is an "industrial-strength" version of the NQTHM or Boyer/Moore theorem prover, and has been used for the formal verification of commercial microprocessors, the Java Virtual Machine, interesting algorithms, and so forth.
ClearLisp is a Common LISP interpreter written in C# with the purpose of scripting in a .NET or Mono environment. The ClearLisp language supports a large subset of CL and has an object model with generic functions, class and instance methods, properties, and import of existing .NET classes. ClearLisp executes LISP scripts in interactive mode or in Web mode (IIS; XSP or Apache with Mono). Sample ClearLisp code is provided in the form of a personal, file-based wiki Web application.