CMUCL is a free implementation of the Common Lisp programming language which runs on most major Unix platforms. It mainly conforms to the ANSI Common Lisp standard. Here is a summary of its main features:

• a sophisticated native-code compiler which is capable of powerful type inferences, and generates code competitive in speed with C compilers.
• generational garbage collection and multiprocessing capability on the x86 ports.
• a foreign function interface which allows interfacing with C code and system libraries, including shared libraries on most platforms, and direct access to Unix system calls.
• support for interprocess communication and remote procedure calls.
• an implementation of CLOS, the Common Lisp Object System, which includes multimethods and a metaobject protocol.
• a graphical source-level debugger using a Motif interface, and a code profiler.
• an interface to the X11 Window System (CLX), and a sophisticated graphical widget library (Garnet).
• programmer-extensible input and output streams.
• an Emacs-like editor implemented in Common Lisp.
• freely redistributable: free, with full source code (most of which is in the public domain) and no strings attached (and no warranty). Like the GNU/Linux and *BSD operating systems, CMUCL is maintained and improved by a team of volunteers collaborating over the Internet.

What is Common Lisp?

Common Lisp is well suited to large programming projects and explorative programming. The language has a dynamic semantics which distinguishes it from languages such as C and Ada. It features automatic memory management, an interactive incremental development environment, a module system, a large number of powerful data structures, a large standard library of useful functions, a sophisticated object system supporting multiple inheritance and generic functions, an exception system, user-defined types and a macro system which allows programmers to extend the language.

Pascal is for building pyramids -- imposing, breathtaking structures built by armies pushing heavy blocks into place. Lisp is for building organisms ...
Alan Perlis