https://pharo.org/news/2024-04-26-pharo12-released.html
Pharo is a pure object-oriented programming language and a powerful environment, focused on simplicity and immediate feedback (think IDE and OS rolled into one).
How does it compare to common lisp? IMO that's the gold standard for immediate feedback and interactive development.
It's a Smalltalk. I do not like to compare languages because each one has its own merits, but until now, I do not think there is an environment that matches what Smalltalk (and Pharo) provides (which is just understandable by using it, heh)
You can try also https://gtoolkit.com/ The language is the same of Pharo, but the GUI is better, IMHO.
Glamorous Toolkit/Pharo are better than CL as IDE/GUI. It is more like a "video-game", because the IDE is a first class citizen and you can customize it. For example you can notice if some classes are not passing some tests, because there are flags in the IDE.
As language I prefer CL, because metaprogramming (i.e. macro) are more explicit and clear respect Smallatalk approach.
In CL you have something like "(some-dsl-prefix ...)" and all the things following the "(some-dsl-prefix ...)" are clearly is the specified DSL. You can expand the macro, for seeing its semantic.
In Smalltalk you had to check the metaclass that created the object, but objects can be created in different point respect their usage, so good luck. Then you had to inspect if the behavior of some standard method is modified/customized. CL macro run at compile-time, while Smalltalk metaprogramming code run at run-time, using reflection, and customization of metaclasses.
A CL macro has a better view of the DSL code, because it can walk in it. I don't remember how Smalltalk solves this.
I tried Smalltalk few years ago, so maybe I missed something.
We've had to work in Pharo for our OOP uni course, and it was one of the worse experiences I've had in school. Mind you, it was something like 7 years ago, so the language may very well be a lot better now, but the whole "your IDE is the code" felt cubersome, it was buggy and crashed randomly, and in general I spent more time fighting with the IDE than doing something useful.
It was a bad time, but also a great learning experience. Being forced to work in something that IMO sucks is an useful skill, but I never want to see that language again :D