A lightweight common lisp interpreter and compiler, which compiles to bytecode, and runs on Windows, AmigaOS, Acorns, OS/2 and most flavours of Unix. CLISP is licensed under the GNU GPL.

An interpreter and optimizing compiler to native code running on a few flavours of Unix (including x86/FreeBSD, x86/Linux and sparc/Solaris). CMUCL can be difficult to compile; it requires itself to build itself, and bootstrapping is an issue. CMUCL is mostly public domain software, though portions are under an X-like or BSD-like licence.

Corman Lisp is a compiler for Windows 95/98/2000/ME/NT, with integration with the Windows API. Corman Lisp is free for personal use.

Standing for Embeddable Common Lisp™, ECL is an implementation of Common Lisp running on at least x86, Sparc and PPC architectures, under Linux, FreeBSD, Solaris, MacOSX and Windows (using the cygwin environment). As well as a bytecode compiler, ECL can compile to C. ECL is licensed under the GNU LGPL.

GNU Common Lisp™ has languished in the past as a non-ANSI compliant Common Lisp; recent times have let it see more developments towards supporting the ANSI Common Lisp standard. It cannot (yet) be recommended as a Common Lisp, but it is still useful for running software written for it (primarily Maxima and Axiom). GCL is licensed under the GNU LGPL.

OpenMCL is an opensourced Common Lisp implementation derived from MCL 4.2, and runs on MacOS X and Linux/PowerPC. It includes a bridge to the Cocoa framework that allows convenient manipulation of Objective C objects in CLOS. OpenMCL is licensed under the GNU LGPL.

Poplog is an incrementally-compiled runtime that includes a Common Lisp implementation, an ML implementation and a Prolog implementation, all cohabiting in the same image. It is licensed under an XFree86-style license. Poplog CL is not actively maintained.

SBCL is a fork from CMUCL aimed at improving the maintainability by removing the bootstrapping issues involved in recompiling. It runs on many Unix and Unix-like systems (including Mac OS X). SBCL is licensed in a similar fashion to CMUCL: mostly in the Public Domain, with some BSD-like and MIT-like portions.

Franz Inc's Allegro Common Lisp is a fine lisp development environment. See their website for more details.

LCL (formerly Liquid Common Lisp) is an offering from Xanalys.

Another offering from Xanalys, LispWorks has a different set of extensions above the ANSI specification from LCL.

A commercial implementation of Common Lisp for the Macintosh.

A commercial natively multithreaded implementation of Common Lisp for various Unixes.

A non-normative transferral of the official ANSI standard for Common Lisp to the hypertext medium, by Kent Pitman.

The website of the association of lisp users. Infrequently updated.

An on-line Wiki-equivalent with emphasis on Free software written in Common Lisp.

Aggregator for the weblogs and diaries of various Common Lisp hackers.

Home to a number of Common Lisp development projects.