CMUCL is a free Common Lisp implementation, originally developed at Carnegie Mellon University.

CMUCL runs on most Unix-like platforms, including Linux and BSD; there is an experimental Windows port as well.

Early CMUCL releases did not support Intel's x86 architecture due to a lack of registers.

After CMU canceled the project (in favor of a Dylan implementation using some of CMUCL's compiler base) maintenance has been taken over by a group of volunteers.

Around the same time a port to Intel's x86 architecture was completed, first running on FreeBSD, later Linux.