I wanted to try this on my laptop, but the only existing Linux implementation I could find involves recompiling the X11 keyboard driver, which is... not easy.So I've written one that uses evdev/uinput and runs in userspace. It's trivial to compile and it works both for X11 and in the Linux console. I've just got a very simple keymap in it to try, hopefully someone else finds it useful.You can find it here: https://github.com/abrasive/spacefn-evdev Logged

I use, and can highly recommend, the Left Alt key. The Alt keys are well-placed for GuiFN-like modifiers, albeit more so on some keyboards than others. You basically want a key on the bottom row that's easy to press with the thumb. The Alt keys make decent thumb keys and I consider it to be a terrible waste not to use them for something more useful. GuiFN operations work best IMO with a left-hand key, and that's why I propose Left Alt rather than Right Alt/AltGr. Also it avoids any problem for those who use AltGr for accented/special characters etc.You may ask: How do I access Left Alt? Well, I simply have moved the function of Left Alt to the Left-Win (Super) key. This setup has the best of both worlds: The convenience of a thumb key but with no need to remap space to be dual-function. Left thumb -> GuiFNRight thumb -> SpaceBoth thumbs have useful jobs.