How can I always have a little window showing me they current keyboard layout? I don't mean the *name* of the layout, I mean a representation of the keyboard and what characters are mapped to each key, something like the output of xkbprint, but changing dynamically when I switch layouts or when I press Shift/AltGr/LevelShift etc.

It would be useful , for example, to know what would appear on the screen when I've switched to a layout I rarely use, such as US International, and not have to do an exhaustive search of the keyboard so I can find how to enter a ß

I could probably figure out how to do it (I'm a kernel guy, not a UI guy, so it would take a while) but I'm hoping something like this already exists.