The FNPCT package
The purpose of this package is to offer kerning for footnote marks, i.e. the superscripts. This is not appropriate for all superscripts. Symbols must be handled differently than numbers. And of course the amount depends on the chosen font. Robert Bringhurst says in The Elements of Typographic Style:
“Superscripts frequently come at the ends of phrases or sentences. If they are high above
the line, they can be kerned over a comma or period, but this may endanger readability,
especially if the text is set in a modest size.”
fnpct can not make this decisions for you. It sets some initial values for the comma and the full stop which looked good to me with the tested fonts. Additionally it kerns the superscripts away from words when it follows directly. The amounts of the kerning can be changed using an option.
As a side effect
fnpct switches the order of the superscript and the following comma or full stop. Additional punctuation marks can be added to the switching behaviour and the amount of kerning can be set for each punctuation mark individually.