Apple had the original PARC Smalltalk but never did anything with it until it evolved into Squeak in 1996, which was Apple's very first open source product. Later two forks went in different directions: Cuis and Pharo.
https://squeak.org/https://cuis-smalltalk.org/https://pharo.org/
Forking Little Smalltalk (an early open source text based Smalltalk) is a rather popular thing to do, so I won't give all the links. A bit more sophisticated is GNU Smalltalk:
https://www.gnu.org/software/smalltalk/
Are there any quality implementations for Java or .NET VMs? One would think that this is the easiest way to get a high-quality GC today. And both ecosystems have some special sauce in them for dynamically typed languages - DLR in .NET, and I'm not sure if there's a single brand for that in Java land, but they've been busy adding features for the likes of JRuby for a while now.
Cincom had previously tested the waters by buying another Smalltalk called Object Studio.
IBM sold its VisualAge Smalltalk to Instanciations: https://www.instantiations.com/products/vasmalltalk/index.ht...
Apple had the original PARC Smalltalk but never did anything with it until it evolved into Squeak in 1996, which was Apple's very first open source product. Later two forks went in different directions: Cuis and Pharo. https://squeak.org/ https://cuis-smalltalk.org/ https://pharo.org/
Forking Little Smalltalk (an early open source text based Smalltalk) is a rather popular thing to do, so I won't give all the links. A bit more sophisticated is GNU Smalltalk: https://www.gnu.org/software/smalltalk/
I consider Self to be Smalltalk, though not Smalltalk-80: https://selflanguage.org/
There are Smalltalks based on Javascript, as well as an alternative VM for Squeak and friends: https://www.amber-lang.net/ https://squeak.js.org/ http://u8.smalltalking.net/
There are probably a few that I missed that are still in use.