sxhkd

Bastien Dejean wrote sxhkd as a companion to bspwm, which on principle doesn't handle the keyboard at all. The window manager takes commands over a socket; sxhkd catches the keys with a grab and runs whatever sxhkdrc says. The split means the same bindings work regardless of window manager.

The config format has one trick that made it popular: brace expansion. The line super + {1-9} with the command bspc desktop -f {1-9} produces nine bindings in one go. Chords ("press Super+W, then R") work too, something that otherwise tends to require a window manager with its own embedded interpreter.