As a long-time Emacs user, I am always a bit amused when I get to explain to someone the basic editing/movement keybindings and how many non-Emacs places they work.

Not just command lines and REPLs, either – the macOS/iOS/iPadOS family of GUI text widgets also support at least a subset of the readline keybindings. For example, I’m writing this on an iPad with a keyboard attached, and can navigate around this textarea, though it isn’t set up to treat Option as Meta, so not all of the standard keybindings work.