During a discussion with my son, we started to wonder how many "non-ASCII" (EDIT: roughly speaking, see below) letters there are in European languages. By "ASCII" here, I mean letters are the "basic" ones in alphabets, the ones you find in the center of a QWERTY or AZERTY keyboard, or the ones "commonly" recognized across European languages.
In French we have two such graphemes: æ and œ. In German there is ß.
Is there a place that references European alphabets through a "common core" and such additions?
Please note that I am not interested in diacretics (é, ł, ñ, ...) but in basic letters that are not present in other alphabets (or only in a very few, for languages that would be really close to each others, but still perceived as separate languages)