I seem to remember a discussions about this a decade ago, with smalltalkers saying that the only big difference is that programmatic generation of code is not so common in ST as it is in ruby (i.e. "attr_*" is possible in ST but doesn't actually exist).

Other than that I _think_ maybe ST has a fixed number of slots per class compared to dynamically added instance/class variables in ruby? My memory is fuzzy.

By the way, there _is_ a ruby built by smalltalk developers[0] exactly because the object model is 99% the same.

[0] http://maglev.github.io