Clozure CL was forked from Macintosh Common Lisp (MCL) in 1998 and the development has been entirely separate since. 
When it was forked from MCL in 1998, the new Lisp was named OpenMCL. Subsequently, Clozure renamed its Lisp to Clozure CL, partly because its ancestor MCL has been released as open source.
Clozure thought it might be confusing for users if there were two independent open-source projects with such similar names. The new name also reflects Clozure CL's current status as the flagship product of Clozure Associates.
Get Clozure CL and give it a try to see what it's all about!

What's New in This Release:
· The FASL version changed: FASL file produced with earlier versions of CCL won't work with this version and vice versa.
· Limiting the extent of load-time OPTIMIZE proclamations
· Detecting character encoding/decoding problems
· Condition type signaled by NO-APPLICABLE-METHOD
· New default values for CCL:*DEFAULT-FILE-CHARACTER-ENCODING* and CCL:*TERMINAL-CHARACTER-ENCODING-NAME*
· Access to high-resolution clock
Accessing and manipulating character-encoding names and aliases - New functions:
· (CCL:LIST-CHARACTER-ENCODINGS) returns a list of the "proper" names (keywords) of all defined character encodings.
· (CCL:LIST-CHARACTER-ENCODINGS :INCLUDE-ALIASES T) returns a list of all proper names and aliases of all defined character encodings.
· (CCL:DEFINE-CHARACTER-ENCODING-ALIAS alias existing) Tries to ensure that alias (a keyword) is recognized as an alias for the existing character encoding existing (which can be a CHARACTER-ENCODING object or a keyword that names one)
· (CCL:REMOVE-CHARACTER-EN...