Shell sort is a sorting algorithm created by Donald Shell in 1959 that improves on insertion sort. It works by comparing elements that are farther apart within the array, making multiple passes with smaller increments to sort the array more efficiently than insertion sort. Radix sort is a non-comparative sorting algorithm that sorts integers by grouping keys based on the place value of their digits using counting or bucket sorts. It has linear time complexity, making it very fast for sorting integers compared to other algorithms. Both algorithms are useful for sorting integers but are limited to that data type.