So far it's just a subset of what's supported by SLIME for common lisp, and I've heard the smalltalk community emphasizes interactive development tooling even more so than the lisp folks. I've seen some of the gtoolkit videos and it's really impressive what such a small group of people have built, I'll definitely study it more seriously for ideas for my python environment once I've got the basics finished. I even tried gtoolkit very briefly but got stuck just trying to show all keyboard shortcuts in a given context and add new ones, but that was years ago and a quick search says Pharo's redone it's shortcut system since then.