The ones that compile to native code: - Lispworks (commercial) - Allegro CL (commercial) - SBCL (my pick) - CMUCL - OpenMCL (Mac only) - GNU CL (not stand

The ones that compile to native code: - Lispworks (commercial) - Allegro CL (commercial) - SBCL (my pick) - CMUCL - OpenMCL (Mac only) - GNU CL (not standard-comforming, but works well with other GCC binaries) - Corman CL (commercial, windows only) This is just off of the top of my head, please add anything I've missed. Assuming you're doing web apps: http://groups.google.com/group/comp.lang.lisp/msg/352f440baa7aeb94 http://groups.google.com/group/comp.lang.lisp/msg/352f440baa7aeb94 They (cl-user.net) have pretty impressive results with a single Lispworks process in a production environment; ~3.3 requests/sec, ~5million requests/day, uptime 456 days. It seems that historically when you want performance+portability+paid-support you go for one of the commercial implementations. CMUCL used to be the choice among free implementations for performance. SBCL inherits the performance of CMUCL, and they reworte some of the layers to be more portable. They had some threading issues in FreeBSD, but they're now resolved and pretty solid after recently passing version 1.0. SBCL now has a pretty substantial user base, so you should be able to get help by just asking around.