Be aware, though, that the newest version (Karabiner-Elements) has a bug where a key might get stuck. Which means you won't be able to login if SHIFT or a letter is stuck. I eventually removed it, because I lost work a few times because of this.
Re:Enabling the F4 key in macOS
by egypturnash on Friday November 24, 2017 @11:39AM
(#15771672)
Works fine for me. Though I don't remap shift or any letters.
I prefer Hammerspoon to be honest. It's free, open source and you can modify pretty much everything on your Mac. Be it key bindings, hotkey sequences or automation of other software's behaviour and so on.
I use 'em both. Hammerspoon is amazing, however Karabiner nowadays has a nice GUI for remapping your keys. This makes for an extremely low entry.
As an aside, the original Karabiner developer has a donation page here: https://pqrs.org/osx/karabiner/pricing.html
I use it to turn |\ into forwards delete (with fn \ emitting a \) and to turn caps lock into cmd-alt-shift. You can do some really crazy things with it if you’re sufficiently dedicated.