[floatboth]

Remapping it to Control is easy to do natively in macOS. What you can do with Karabiner is Control/Escape: http://stevelosh.com/blog/2012/10/a-modern-space-cadet/#cont...

For X11, there's xcape: https://github.com/alols/xcape

For Windows, of course, AutoHotKey (my config: https://github.com/myfreeweb/dotfiles/blob/master/windows/ke...)