off the top of my head, gamma world, mutant crawl classics, Mutant (and its more modern version mutant year zero).
Mutants and masterminds depending on your definition of mutation, since its more like “superhero marvel mutants” than like “radioactive mutants”
Monte cooke games also has a 5e supplement called “arcana of the ancients” that includes mutation rules that are pretty good IMO.
I dont know if it will include it, but i am like 90% sure the upcoming mystic punks from exalted funeral is going to have something to do with mutants.


























Brandon’s bard in a box from 2e.