[pkamb]

What application do you use to set this up on a Mac?

[ZeroGravitas]

Karabiner does the actual remapping.

https://karabiner-elements.pqrs.org/

and

https://github.com/yqrashawn/GokuRakuJoudo

lets you write your keymappings in a text editor and translate it into the weird XML/JSON syntax so you don't have to use the GUI editor.