See Implementations for current Common Lisp implementations.

Defunct Commercial Common Lisps

Sapiens Software Corporation

Star Sapphire Common LISP. MS-DOS. Free to download for non-commercial personal use. Copyrighted unsupported shareware.

Gold Hill

Golden Common Lisp: Windows. Status unknown.

Lucid Common Lisp

Now maintained as Liquid Common Lisp by LispWorks

Defunct Open Source Common Lisps

WCL

Unix, I don't know about the status of this implementation

It's apparently a CLtL1. -- Paul Dietz

Parrot Common Lisp

Parrot virtual machine. Attempt to write a Common Lisp for the Perl 6 Virtual Machine. Never finished