Allegro Common Lisp is a commercial implementation of the Common Lisp programming language developed by Franz Inc. Allegro CL provides the full ANSI Common Lisp standard with many extensions (threads, CLOS streams, CLOS MOP, Unicode, SSL streams, implementations of various Internet protocols, OpenGL interface and more). The first version of Allegro Common Lisp was finished at the end of 1986, originally called Extended Common Lisp. Allegro CL is available for Windows, Linux, Mac OS X and various Unix platforms, supporting 32 or 64 bits. Internationalization support is based on Unicode. It supports various external text encodings and provides string and character types based on UCS-2. Allegro CL can be used with and without its integrated development environment (IDE), which is available for Windows and Linux, and on Mac OS X in version 8.2. The IDE (written itself in Allegro CL) includes various development tools like an editor and an interface designer. Allegro CL can be used to deliver applications.
Allegro CL is available as a Free Express Edition (with some limitations like a limited heap space) for non-commercial use. Customers can get access to much of the source code of Allegro CL.