I'm using on X11 https://github.com/sezanzeb/input-remapper (currently 2.4k stars)

"Supports X11, Wayland, combinations, programmable macros, joysticks, wheels, triggers, keys, mouse-movements and more."

My use cases are:

- System wide VIM like key mapping

- Access umlauts from my US-keyboard layout

- Key remapping

It's also working great to remap the 10+ buttons of a razer naga mouse