Elixir REPL in production yeah. Not to modify anything, but to inspect the state of the world and figure out why some OTP apps were dying. I'm drawing a blank on the name of the build tool, but the "launch binary" it produces has an option to fire up a second copy of your app, keep the console alive, and connect it to the cluster as another node. Worked like a charm, although it's something I wouldn't want to do on a regular basis :)