Free Windows keyboard driver that extends AltGr to provide comprehensive accented character support (including multi-accented characters), international punctuation, IPA, medieval characters, mathematical and non-mathematical symbols, and more.
Designed for UK keyboards and installs as a regular keyboard layout option. I might adapt it for US keyboards if there's enough interest.
The driver should be stable (built using MSKLC, which is mature) but classified as beta because it has not yet...