The best CL implementations unfortunately are not opensource. There is still a large use of Lispworks by many heavy CL developers. And anyone who has used it knows what they have to offer over the opensource equivalents. Support is something well worth its cost. Plus in production things tend to just work on Allegro and Lispworks. They tend to bench well for the things we need. http://ftp.linux.org.uk/~ober/report.html