The old joke with Common Lisp used to be if you've developed a program for one version of Common Lisp, you've developed a program for one version of Common Lisp

The old joke with Common Lisp used to be if you've developed a program for one version of Common Lisp, you've developed a program for one version of Common Lisp. Lisp is notoriously hard to deploy. Code is not portable between different lisp implementations. Apple's ATG ended up axing many projects because they had so much trouble moving their lisp from 680x0 to PowerPC. The fact you talk about "your system's package manager" ignores my point -- I'm not saying Lisp is especially hard to deploy to servers (although it is -- but this is, as you say, a popularity issue; and it would be far worse if the world of servers hadn't converged on a small number of very similar platforms). I'm saying it's hard to deploy to desktops and mobile, which is where most of the "useful" programs people might want to write still live. A huge part of Lisp's problem is fragmentation. Which Lisp? Aside from fragmentation in Common Lisp itself, there's all the not-quite-Lisps around, ranging from Arc to Scheme to Clojure to sheesh-I-really-have-no-idea. And of course this is because once you start coding in Lisp there's an overwhelming urge to abstract away difficult things in your own clever way, perhaps even hacking the language itself, and pretty soon your little world is utterly unique. Another great, simple language in the exact same boat is Forth.