A debugger! Thank you!! Step-by-step debuggers are crazy useful for beginners, yet most small IDEs targeted at beginners/non-programmers don't have them. Especially when dealing with loops and recursion, stepping through and seeing the values change and stack grow is invaluable for learning how a program executes and makes finding issues less frustrating.

I'm on a phone right now so I can't try it, but does it by any chance allow evaluation in the paused state? That's also been pretty handy for me when teaching beginners.