2023-02-25:
It has been more than a year now that I no longer have Apple hardware. I am using Linux exclusively and I do not anticipate the situation changing in the foreseeable future, therefore I'm unable to keep updating the macOS port and I'm forced to archive it for now. I could still accept submissions, but I have a policy of not publishing anything I don't use or can't test myself.
Don't let it discourage you, though; unless you benefit from the changes made in version 1.3 (in beta for many years now — it might as well be considered released de facto at this point) the layout you'll find here remains as useful as ever and will not "rot", at least not until Apple decides to break the keyboard layout format in a future version of macOS.
The Keyboard Layout for Europeans, Coders and Translators - Version for Mac OS X.
This is a port of the EurKEY Keyboard layout, which features a QWERTY baseline layout (=good access to braces etc.) with quick access to commonly used accented characters and Umlauts.
Status: The whole layout should be mapped now. Please report if you find any missing characters.
Copy the two files EurKEY.keylayout and EurKEY.icns to your library, either system-wide (/Library/Keyboard Layouts) or for your local user (~/Library/Keyboard Layouts). A system-wide installation is preferred though to ensure the layout is available to all applications. (See also this Superuser answer.)
The Layout itself is licensed under GPLv3. The EU flag icon is taken from Iconspedia, created by Alpak and licensed under CC