NugKeyFeedback

A single button that mirrors whatever you currently press.

Masque skin from demo

If used with Bartender/Neuron/ElvUI you'll need to enable 'Cast on Key Down' feature

If you ever tried hiding the action bar, you probably discovered that not seeing your key presses feels kinda bad.
This can act as a small HUD action bar.
Can be useful for streamers too, i guess.