I have been using Pharo as the backend for my turn-based game. It is such a relief to have the always ready live environment. Together with Flutter (another live env) I can create new backend services in a matter of minutes. For example: in Pharo I just add new field to the response. In Flutter app, without any restarts, I debug the REST call, check the response, modify my inner objects to accept this new field and boom, client and server can talk to each other again! Plus in Inspector I can watch the data changes after each REST calls. I do not have to issue an sql query or stop server in debug mode and recall the REST in order to catch breakpoint. The Inspector window is always there!
All this is done without any restarts of the server/client app. I have even created a smalltalk-to-dart code generator:
https://github.com/gladimdim/smalltalk-to-dart. It serializes Pharo objects into the Dart class definitions with all fields and even with the fromJson methods!