[im_down_w_otp]

Emacs. The whole thing is a bunch of running scripts, and you can manipulate all of it almost an way that you like. Add your own, muck with the ones that are there, even screw with things that are actively running.

[maybeok]

Emacs is nice way to discover live-action coding against a running process. Design time, dev-time, compile-time, and run-time all mesh into one.

Everybody needs to give a live-action language like Smalltalk or lisp a try at least once.