none (in the way of the language). like was said:
Nominative --- Masc: ein | Fem: eine | Nt: ein
Accusative --- Masc: einen | Fem: eine | Nt: ein
for nominative and acusative in neuter and feminine there is no difference. only maculine that differs.
Don't you rather mean the difference between eine/one and eine/a? It lays in the meaning: "one" as only one thing in comparison to two things (called numeral) or "a" as anything/anyone (called indefinite article) in comparison to the definite article "the".
All nouns ending in "-ung" are feminine. In German, "things" can be masculine or feminine as well, not just neuter.