Search for a useful interactive programming environment
I am not too worried about language. I am just looking for a nice
  interactive learning environment, that combines the best of REPL and
  editing. Can you tell me of anything that you use or know of?


Runestone Academy has a component called ActiveCode that allows you write Python code and run it. It also has a slider so that you can go back to earlier versions of your source code to review and run.

In addition to activecode, you can also execute Python code with the assistance of a unique visualization tool. This tool, known as codelens, allows you to control the step by step execution of a program. It also lets you see the values of all variables as they are created and modified. 

There is a lot more to the web site but is what I use to help others learn Python 3 and the nicest part is that once the students get the hang of the e-books they tend to take off at their own pace.