ControllerMate is another really powerful tool, though not just for keyboards but for USB devices in general. Interface is a bit funky but it's really worth checking out, not just mapping but conditional reactions, timing, scripting, for any key or arbitrary combinations of keys or non-keyboard devices (I made a DS4 work with a Mac at launch except for the touchpad part of it for example).

Ooo, interesting! I'll definitely look into that when I go into one of my next "optimize my workflow as a form of procrastination" mindsets I tend to end up in