Steel Bank Common Lisp (SBCL) is a high performance Common Lisp compiler. It is open source / free software, with a permissive license. In addition to the compiler and runtime system for ANSI Common Lisp, it provides an interactive environment including a debugger, a statistical profiler, a code coverage tool, and many other extensions.
Clozure CL (often called CCL for short) is a free Common Lisp implementation with a long history. Some distinguishing features of the implementation include fast compilation speed, native threads, a precise, generational, compacting garbage collector, and a convenient foreign-function interface.
Armed Bear Common Lisp (ABCL) is a full implementation of the Common Lisp language featuring both an interpreter and a compiler, running in the JVM. Originally started to be a scripting language for the J editor, it now supports JSR-223 (Java scripting API): it can be a scripting engine in any Java application. Additionally, it can be used to implement (parts of) the application using Java to Lisp integration APIs.
CLISP is a Common Lisp implementation by Bruno Haible, then of Karlsruhe University, and Michael Stoll, then of Munich University, both in Germany. It implements the language described in the ANSI Common Lisp standard with many extensions.
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.
ECL is an implementation of the Common Lisp language as defined by the ANSI X3J13 specification. it also has an iOS port.
Allegro CL ® is the most powerful dynamic object-oriented development system available today, and is especially suited to enterprise-wide, complex application development.
LispWorks ® is an implementation of ANSI Common Lisp running on Windows, Linux, Mac OS X, FreeBSD, x86/x64 Solaris, SPARC/Solaris and HP-UX.
mocl™ allows you to create applications for iOS, Android, and other mobile platforms using highly expressive Common Lisp code. mocl makes this possible by compiling your Common Lisp code to platform-portable, efficient C code.