The Smalltalk books were a big influence on me when they came out, so I was happy when a company I was working for sublet space from Xerox PARC and we had meetings there. :)

Is anybody familiar with the various Smalltalk releases today and willing to do an overview of what's available?

ParcPlace spun off from Xerox to sell the original Smalltalk in 1988 but they sold that to Cincom in the late 1990s: http://www.cincomsmalltalk.com/main/products/visualworks/

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.