I think the best modern example is ObservableHQ [1]. I took a screen shot yesterday when I found myself interleaving runtime, TDD, IDE, debugger and partial recompilation in one window. It blew my mind.
I have never experienced such a productive programming environment. https://twitter.com/tomlarkworthy/status/1345321532650905601...
For there I can change variable at runtime. Change the implementation and have the tests auto run. Correct the tests, set a breakpoint in the test or implementation with "debugger;".
I think it might be more productive than smalltalk because of the spreadsheet-like reactive recomputation. Plus it supports real markup as inline documentation.