CMU Common Lisp is described as 'CMUCL is a free, high performance implementation of the Common Lisp programming language which runs on most major Unix platforms. It mainly conforms to the ANSI Common Lisp standard'. There are more than 10 alternatives to CMU Common Lisp for Windows, Linux, Mac, BSD and Self-Hosted solutions. The best alternative is Hy, which is both free and Open Source. Other great apps like CMU Common Lisp are Steel Bank Common Lisp (Free, Open Source), CLISP (Free, Open Source), Armed Bear Common Lisp (Free, Open Source) and ManKai Common Lisp (Free, Open Source).
Hy is a wonderful dialect of Lisp that’s embedded in Python. Since Hy transforms its Lisp code into the Python Abstract Syntax Tree, you have the whole beautiful world of Python at your fingertips, in Lisp form!
CLISP is a portable ANSI Common Lisp implementation and development environment by Bruno Haible. Interpreter, compiler, debugger, CLOS, MOP, FFI, Unicode, sockets, CLX. UI in English, German, French, Spanish, Dutch, Russian, and Danish.
Allegro CL is the most powerful dynamic object-oriented development system available today, and is especially suited to enterprise-wide, complex application development. Complex applications with billions of objects are now made easy with Allegro CL 9.0.
MIT/GNU Scheme is an implementation of the Scheme programming language, providing an interpreter, compiler, source-code debugger, integrated Emacs-like editor, and a large runtime library. It's best suited to programming large applications with a rapid development cycle.