There’s an interesting article over at Prodtyping that illustrates how to implement a global Hyper key on the Mac. By “global” I mean it works everywhere, not just Emacs. The idea is to use Hyper as a global shortcut key. The article shows the setup for making the Caps Lock serve as Hyper and uses it to launch Atom, Chrome, or iTerm.
The method uses Karabiner/Hammerspoon to do the key mapping and to fire off the appropriate application based on the key that Hyper is modifying. That last step requires a bit of Lua but Prodtyping shows a template that you can use to start your own application choice.
Evan Travers has a similar post that discusses using Hammerspoon to create and map a Hyper key. If you’re running a Mac and are interested in setting up a universal shortcut key, both posts are worth reading.
I use function keys to switch between my frequently used apps and within Emacs I have the fn key mapped to (Emacs’) Hyper. That works well for me but if you’re looking for a more general solution and you’re on a Mac, the solution in the two posts may be a good one.