I love the system in Autodesk Animator (now: https://github.com/AnimatorPro). Every menu item or button currently on the screen always have a unique initial letter. There is no need to highlight or underline anything. Amazingly this was done without having to use any too obscure labels (but I doubt it would be fun to try to translate it to other languages). Almost every function is two or three single letter key-presses away, and after using the application for a while you will have memorized more and more of those.

Some frequently used functions have their own special single-key shortcuts as well, so instead of having to press C-P (to open the Clip menu and then select Paste) you can just press the ' key, saving the user a key-press every time they do that.

I recently rediscovered that I can do GUI menu things on the keyboard in apps like VLC. Feels like a magic trick -- the best of both worlds. Was it the move to phones that did it? Or did most people not use alt shortcuts?

Doesn't work with internationalization. P for Pencil is great in English. P for Crayon en Français? Non.

Doesn't work with reassignable keys, either. If I wanna reassign the shortcut for "pencil" to "d" because it's easier to hit with my left hand then that's my own business.