[ziotom78]

You're right, US keyboards do not support AltGr! I have always used european keyboards and every one of them supports AltGr, so I assumed that US keyboards did the same.

Just for testing, I installed a few new keyboards on my KDE desktop, and I can confirm that French, German, Spanish, and Greek keyboards have support for AltGr combinations to get superscripts/fractions/other characters.

I've never required that a keyboard could allow any character. However, this is indeed possible today, as Shift+Ctrl+u+HexNumber allows to quickly insert any Unicode character. (This works under Xfce and KDE, and probably other DEs.)

Nevertheless, I think that a 100-and-more-keys keyboard should support a subset of the most useful ones. I am a physicist and an Italian, so having quick keyboard combinations for exponents, fractions, and the euro sign € is extremely handy for my everyday activities.

[untoreh]

I think what you are looking for is the us international keyboard layout, which has support for altgr combinations