CMU Common Lisp

CMUCL is a free Common Lisp implementation, originally developed at Carnegie Mellon University. It compiles to native code as well as compact byte code; the compiler ("Python", not to be confused with the Python programming language) generates some of the fastest object code of any Common Lisp implementation. CMUCL runs on most Unix-like platforms, including Linux and BSD; there is an experimental Windows port as well. Steel Bank Common Lisp is derived from CMUCL.

[edit] 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.