Allegro is the only Lisp with a RAD like GUI designer. Other than that, the IDE is alright but I hate how outdated it looks (they don't even have syntax highlig

Allegro is the only Lisp with a RAD like GUI designer. Other than that, the IDE is alright but I hate how outdated it looks (they don't even have syntax highlighting and they expect me to put up with an ugly X11 app on macOS). Allegro's selling point is definitely not the IDE and I very much prefer Slime over it. LispWorks also has an interface builder but only works on Windows I'm afraid. I wouldn't say their IDE offers much over Slime if you are a power user, but I really like their function/class browser over using all the slime-who-* commands and how easy to use their debugger is. What sets it apart is that thanks to CAPI it is trivial to build graphical user interfaces to make your own development experience a bit nicer: for example opening up a filesystem dialog instead of asking the user to retype a string, building a graphical monitor to provide insights on the performance of your Lisp image... You get the picture. It feels very Smalltalk-ish.