My post “A useful Caps Lock key”—based on a method pointed out by Steve Losh—has been one of the most popular pages on this blog over time (up there with nvALT and iTextEditors). It turns your Caps Lock key into a “Hyper” key that emulates holding Control, Option, Shift, and Command all at once, which is handy for expanding your keyboard shortcut collection.
This is a companion discussion topic for the original entry at https://brettterpstra.com/2015/12/18/a-hyper-key-that-can-still-yell