Taking a brief look at my current project of implementing Erlang/Scala style actors in Common Lisp.
The object system in Common Lisp has something that almost no one else does: generic methods. Also called multi-methods, these allow a flexible and safe approach to dynamically adding functionality to a class at runtime. It's monkey patching without the monkey. When I write my programming language in a few decades, these are going to be there.
Software engineer, technical leader, sci-fi reader, and so on. Born in NC, living in SF, and glad to grab a coffee.