The latest MCL version is 5.2, which is a open source Lisp platform now.
MCL 5.2 cannot run on Intel Macs. On 2009, a modified MCL called RMCL (Rosetta-based MCL) is published by Clozure Associates, this new version can run on Intel Macs as well. Now MCL user community is active again.
People can download latest MCL/RMCL at its Google Code site.
Common Lisp implementation